Marketing and

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Federal Grain

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Washington, D.C.

September 2016

StoredGrain 

Insect 

Reference
Stored Grain Insect Reference September 2016

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Abstract

Five primary pests cause most of the insect damage to grain in storage and shipment. These are 

the granary weevil, the rice weevil, the maize weevil, the lessor grain borer or Australian wheat 

weevil, and the Angoumois grain moth. Other insect species or groups of species described in 

this handbook can cause great damage to grain if storage conditions are unusually favorable for 

their increase. Yet, if grain in the unbroken kernel remains unaffected by the five primary pests, 

it is not likely that any other insect will damage it appreciably in commercial storage or shipment, 

except possibly the khapra beetle. The secondary pests are mostly surface feeders in both the 

adult and larval stages. Some of them may eat into kernels of grain and lie hidden there, but most 

of them feed on grain dust or broken surfaces of kernels exposed by either mechanical injury 

to the grain in handling or by feeding of the five primary grain pests with which they are usually 

associated. Therefore the secondary pests can be largely removed by grain-cleaning operations.

Except for the lessor grain borer, the larvae or grubs of the primary insect pests are not ordinarily 

capable of a free existence outside the kernel. they live entirely within the kernel, where they feed 

unseen and usually unsuspected. They cannot be removed by ordinary cleaning machinery and 

must be controlled by other means.

Prepared by the

Federal Grain Inspection Service

United States Department of Agriculture

This reference slightly revises Agricultural Handbook 500, “Stored-Grain Insects” which 

superseded Farmers’ Bulletin 1260, “Stored Grain Pests.” 

Released March 2015
Stored Grain Insect Reference September 2016

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Contents

Stored-Grain Insect Reference

INTRODUCTION .........................................................................................................................5

GRAIN WEEVILS .........................................................................................................................5

Granary Weevil .........................................................................................................................6

Rice Weevil .................................................................................................................................7

Maize Weevil .................................................................................................................................7

Broadnosed Grain Weevil ......................................................................................................... 9

Coffee Bean Weevil .........................................................................................................................9

GRAIN BORERS .......................................................................................................................10

Lesser Grain Borer .......................................................................................................................10

Larger Grain Borer .......................................................................................................................12

GRAIN MOTHS .......................................................................................................................13

Angoumois Grain Moth ...............................................................................................................13

Pink Scavenger Caterpillar ....................................................................................................... 15

European Grain Moth ...............................................................................................................16

Rice Moth ...............................................................................................................................17

FLOUR MOTHS .......................................................................................................................18

Indian Meal Moth .......................................................................................................................18

Mediterranean Flour Moth ....................................................................................................... 19

Meal Moth ...............................................................................................................................20

GRAIN AND FLOUR BEETLES ............................................................................................... 23

Cadelle .......................................................................................................................................23

Sawtoothed Grain Beetle ....................................................................................................... 25

Merchant Grain Beetle ...............................................................................................................25

Squarenecked Grain Beetle ....................................................................................................... 26

Foreign Grain Beetle ...............................................................................................................27

Mexican Grain Beetle ...............................................................................................................27

Siamese Grain Beetle ...............................................................................................................28

Flat Grain Beetle .......................................................................................................................29

Rusty Grain Beetle .......................................................................................................................30

Confused Flour Beetle ...............................................................................................................30

Red Flour Beetle .......................................................................................................................31

American Black Flour Beetle ....................................................................................................... 32

Longheaded Flour Beetle ...............................................................................................................34

Slenderhorned Flour Beetle ....................................................................................................... 34

Smalleyed Flour Beetle ...............................................................................................................34

Depressed Flour Beetle ...............................................................................................................34

Broadhorned Flour Beetle ....................................................................................................... 35

Larger Black Flour Beetle ....................................................................................................... 36
Stored Grain Insect Reference September 2016

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EGGS OF FLOUR AND GRAIN INSECTS ............................................................................... 37

MEALWORMS ...............................................................................................................................38

Yellow Mealworm .......................................................................................................................38

Dark Mealworm .......................................................................................................................40

Lesser Mealworm .......................................................................................................................40

Black Fungus Beetle ...............................................................................................................41

Redhorned Grain Beetle ...............................................................................................................41

DERMESTID BEETLES ...............................................................................................................42

Black Carpet Beetle .......................................................................................................................42

Trogoderma Beetles ..................................................................................................................................................................................................42

SPIDER BEETLES .............................................................................................................................. 46

Hairy Spider Beetle .......................................................................................................................46

Whitemarked Spider Beetle ....................................................................................................... 46

Brown Spider Beetle ...............................................................................................................47

Other Spider Beetles ...............................................................................................................47

MISCELLANEOUS BEETLES ............................................................................................... 48

Twobanded Fungus Beetle ....................................................................................................... 48

Hairy Fungus Beetle ...............................................................................................................48

Corn Sap Beetle .......................................................................................................................49

Cigarette Beetle .......................................................................................................................49

Drugstore Beetle .......................................................................................................................50

Catarama Beetles .......................................................................................................................50

Murmidius Beetle17 .......................................................................................................................51

BOOKLICE OR PSOCIDS ....................................................................................................... 53

SILVERFISH ...............................................................................................................................54

COCKROACHES .............................................................................................................................. 55

FLOUR OR GRAIN MITES .............................................................................................................................. 56

PARASITES OF GRAIN PESTS ............................................................................................... 58

HOW GRAIN BECOMES INFESTED ....................................................................................... 62

HOW TO PREVENT OR REDUCE PRIMARY INFESTATION .............................................. 63
Stored Grain Insect Reference September 2016

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STORED-GRAIN INSECTS

INTRODUCTION

Since the establishment of Federal standards for grain under the pro-visions of the Grain 

Standards Act, Federal grain supervisors and federally licensed grain inspectors have been 

required to identify the various species of “live weevils and other insects injurious to stored grain” 

which may be present in the grain. For accurate identification, uniform names should be used by 

all interested persons, including shipper, purchaser, and elevator operator.

Of the five primary insect pests, the granary weevil, the rice weevil, the maize weevil, and the 

lesser grain borer may well be called grain weevils. The fifth primary pest, the Angoumois grain 

moth, so destructive to wheat and corn, may be called a grain moth. Other insects likely to be 

found in grain may be called simply beetles, moths, and meal-worms. Their presence usually does 

not indicate a condition likely to affect the grain trade, if the grain, after it has reached the elevator, 

is screened and fanned to remove these insects.

This handbook briefly describes the biology, life histories, and habits of stored-grain insects and 

gives effective methods for the prevention and control of grain infestations.

Grain weevils, grain borers, grain moths, flour moths, grain and flour beetles, mealworms, 

dermestid beetles, spider beetles, miscellaneous beetles, booklice or psocids, silverfish, 

cockroaches, flour or grain mites, and parasites of grain pests are discussed.

GRAIN WEEVILS

Of the five true weevils that attack grain in the United States, only three are of primary 

importance—the granary weevil, the rice weevil, and the maize weevil. Except locally, the 

broadnosed grain weevil and the coffee bean weevil are of minor importance. All but the coffee 

bean weevil have elongated beaks or snouts, as shown in figures 1, 3, and 4.
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Granary Weevil

The granary weevil, Sitophilus granarius (Linnaeus),1 is a small, moderately polished, blackish or 

chestnut-brown beetle (fig. 1A). The head emends into a long slender snout with a pair of stow 

mandibles or jaw at the end. This insect is not more than three-sixteenths of an inch long arid 

often is smaller, There are no wings under the wing covers, and the thorax is well marked with 

longitudinal punctures, two characteristics that distinguish this insect from the closely related rice 

weevil with which it is often found.

The granary weevil. one of the oldest known insect pests. has been earned bike commerce to 

all parts of the world. It prefers a temperate climate and is more frequently found in the Northern 

States than in the South.

Both the adults and larvae feed voraciously on a great variety of grains. The adult weevils live, on 

an average 7 to 13 months. and each female lays 50 to 250 eggs during this period. Before laying, 

the female uses her mandibles to bore a small hole in a grain kernel. She then deposits an egg 

through the hole and covers it with a gelatinous fluid that seals the hole. The small, while. fleshy, 

legless grub or larva hatches from the egg and burrows about inside the kernel. When fully grown. 

the larva transforms into a pupa and then into an adult.

In warm weather, the granary weevil develops from the egg to the adult stage in about 4 weeks. 

Cold weather greatly prolongs The developmental period.

Figure 1. Grain weevils: Left, Granary weevil adult; center, Rice weevil adult, right, Maize weevil adult.

 

1

 Coleoptera, Curculionidae.
Stored Grain Insect Reference September 2016

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Figure 2. An ear of corn badly damaged by maize weevils. The ear was hit against a table to jar 

loose a dry powdery substance. or farinaceous material, to reveal the great amount of damage done.

Rice Weevil

The rice weevil Sitophilus oryzae (Linnaeus),1 is a small snout beetle which varies in size, but it 

averages about three thirty-seconds of an inch in length. It varies from reddish brown to nearly 

black and is usually marked on the back with four light-reddish or yellowish spots (fig. 1B). The 

rice weevil closely resembles the granary weevil in form but differs in color and markings, and it 

has fully developed wings beneath the wing covers. The thorax is densely pitted with somewhat 

irregularly shaped punctures, except for a smooth, narrow strip extending down the middle of the 

upper (dorsal) side.

This weevil has been known since early times. It is found in all parts of the world where grain is 

used and is one of the worst pests in stored grain. This insect is particularly abundant in warm 

countries, where it breeds continuously and rapidly destroys all unprotected grain.

The adult rice weevils live, on an average, 4 to 5 months, and each female lays 300 to 400 eggs 

during this period. The early life stages are almost identical in habit and appearance to those of 

the granary weevil. During hot weather, the egg, larval, and pupal stages may be passed in as few 

as 26 days. This period, of course, is greatly prolonged during cool or cold weather.

Maize Weevil

The maize weevil, Sitophilus zeamaise Motschulsky, for a long time referred to as the larger strain 

or race of the rice weevil, is now recognized as a distinct species. Although slightly larger, up to 

one-eighth of an inch long, and darker than the rice weevil adult, the degree of variation within 

each species makes them difficult to tell apart (fig. 1C). The thorax of the maize weevil is densely 

and uniformly pitted with round punctures.

It is a common pest of a variety of grain crops and causes tremendous losses to corn in the South, 

reducing the kernels to dry powder and hulls (fig. 2). The adults fly from the granaries to the fields, 

where they start infestations that may continue after harvest and may be especially destructive in 

storage.

The life history and early life stages are similar to those of the rice weevil (fig. 3). The rate of 

development is slightly slower; a minimum of 30 days is required for passing through the egg, 

larval, and pupal stages.
Stored Grain Insect Reference September 2016

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Figure 3. Maize weevil: Left, eggs; center, larva; right, pupa.

Figure 4. Broadnosed grain weevil: A, Full-grown larva; B, pupa; C, adult. Adult is slightly less 

than one-eighth of an inch long.

A B C
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Broadnosed Grain Weevil

The broadnosed grain weevil, Caulophilus oryzae (Gyllenhal),1 is a small, dark-brown snout beetle 

slightly less than one-eighth of an inch long. In form and color, it resembles the granary weevil 

some-what but differs from it and other grain-infesting weevils by having a shorter, broader snout 

(fig. 4C).

The weevil is occasionally found in Georgia and South Carolina and is widespread in Florida, 

where it is a serious pest of stored grains, but it is not found in northern grains. It is unable to 

breed in dry, hard, uninjured grain, but it does attack soft or damaged grain or grain that has been 

attacked by other grain insects. It is a strong flier, and, like the maize weevil, flies to the cornfields 

and infests the grain before it becomes fully hardened.

The adult weevils normally live about 5 months, and, during this time, each female lays 200 to 300 

small white eggs, usually in broken portions of the grain. In a few days, the eggs hatch, and the 

small, white. legless grubs feed on the softer portions of the grain until fully grown (fig. 4A). They 

then transform into white pupae (fig. 4B) and, in a few days, transform into adult weevils which cut 

their way out of the grain. In summer, the period from egg to adult is about 1 month.

Coffee Bean Weevil

Figure 5. Coffee bean weevil adult, 

about three-sixteenths of an inch 

long.

The coffee bean weevil, Araecerus Jasciculatus (De Geer),2

is a very active, robust, dark-brown beetle two-sixteenths to 

three-sixteenths of an inch long. It is covered with a mottled 

light- and dark-brown pubescence. This insect may be easily 

recognized from figure 5.

This weevil is found in many countries and is extremely 

abundant in the Southern States, where it breeds in dried 

fruit, coffee berries, cornstalks, corn, and the seed and seed 

pods of an almost endless variety of plants. The coffee 

bean weevil is a strong flier and is frequently seen in the 

cornfields of the South on exposed and damaged ears. It 

lays eggs in the soft kernels of corn and continues to breed 

after the corn has been harvested and placed in storage. 

This insect does not cause much damage to corn in storage, 

since the corn becomes too hard to be attractive. It may, 

however, be very abundant locally in corn in Florida during 

the first 3 months of storage. This weevil reportedly caused 

total destruction of a sack of kafir seeds in Honolulu. Over 

the country, the coffee bean weevil is a minor grain pest.

 

2

Coleoptera. Anthribidac.
Stored Grain Insect Reference September 2016

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GRAIN BORERS

Three species of grain borers are established in the United States. The lesser grain borer is 

widespread in the grain centers of this country and is a serious pest of stored grain. The larger 

grain borer and the bamboo powderpost beetle are confined to the Southern States and are not of 

commercial importance.

Lesser Grain Borer

The lesser grain borer, Rhyzopertha dominica (Fabricius),3 is one of the smallest beetles of those 

injurious to grain in this country. It is known to many grain dealers as the Australian wheat weevil 

because of the large supplies of infested wheat that were imported from Australia during World 

War I. It is widespread in the Gulf States, and grain samples infested with this beetle arc found 

in all large grain centers. The lesser grain borer is readily distinguished from other grain pests 

by its slender cylindrical form and small size. It is polished dark brown or black. with a somewhat 

roughened surface, and is about one-eighth of an inch long and one thirty-second of an inch 

wide (fig. 6A). The larval and pupal stages are illustrated in figure 7. This grain borer belongs to a 

family of beetles that has the head turned down under the thorax and that is armed with powerful 

jaws used for cutting into wood. Originally native to the Tropics. the lesser grain borer has spread 

through commerce to all parts of the world.

Both the beetles and larvae cause serious damage in warm climates by attacking a great variety 

of grains. Figure 8 shows how destructive they can be to wheat kernels, which, in this case, were 

literally riddled by the boring of the adults and their larvae. The damaged kernels are always 

surrounded by powder from the chewed-up grain.

Each female lays 300 to 500 eggs and deposits them, singly or in clusters, upon the loose grain. 

The eggs hatch in a few days, and the small whitish grubs, or larvae, crawl actively about the 

grain, and feed on the flour produced by the boring beetles or bore directly into grains that have 

been slightly damaged. They complete their growth within the grain, transform into white pupae, 

and, in time, change into adult beetles, which cut their way out of the grain. In summer, the period 

from egg to adult is about 1 month.

Figure 6. Grain borers: Left, lesser grain borer adult; right, bamboo powderpost beetle adult.

 

3

Coleopteni. Bostrichidae
Stored Grain Insect Reference September 2016

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Figure 7. Lesser grain borer: Left, larvae; right, pupa.

Figure 8. Wheat kernels thoroughly riddled and devoured by boring and feeding of lesser grain 

borer and its larva.
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Larger Grain Borer

The larger grain borer, Prostephanus truncatus (Horn),3 is a small, dark-brown, elongatecylindrical beetle about one-sixth of an inch long. It is very similar in appearance to the lesser 

grain borer, but may be distinguished from that insect by its larger sin and comparatively smooth, 

polished surface (fig. 9A).

This tropical insect has limited dis-tribution in this country. It is occasionally found infesting corn in 

the South and has been reported from Texas, California, and the District of Columbia. Similar to 

the lesser grain borer in habits, it belongs to a family of beetles that is mainly destructive to timber. 

Like the lesser grain borer, it has probably acquired the grain-feeding habit rather recently.

Another member of the family, the bamboo powderpost beetle, Dinoderus minutus (Fabricius),3

occasionally infests stored grain in the United States. It has been reported from Louisiana and 

Florida. In general appearance, it resembles the larger grain borer (fig. 6B).

Figure 9. Larger grain borer: A, adult; B, larva; C, pupa; D, antenna of adult.

C A

B

D
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GRAIN MOTHS

The term “grain moth” includes only those moths capable of destroying sound, unbroken grain 

kernels. They are not as abundant as the flour moths, which are principally pests in broken, 

damaged kernels or milled products.

Angoumois Grain Moth

The Angoumois grain moth, Sitotroga cerealella (Olivier),4 is a small buff or yellowish-brown moth 

with a wing expanse of about one-half inch.

This is the moth most commonly found in infested grain in this country, and it is not likely to be 

con-fused with any other grain moth. It attacks all cereal grains, is found in all parts of the world, 

and is particularly injurious in the South, where it attacks grain both in the field and in storage. 

In the North, it survives the winter mainly in the larval form in kernels of grain in storage or in 

scattered wheat in litter, straw piles, and baled straw. The emerging moth flies to the wheatfields in 

May and deposits eggs upon the developing grain.

Under normal conditions, each female lays an average of 40 eggs: although, under favorable 

conditions, individual moths have been known to lay as many as 389 eggs. The eggs, which 

are white when first laid, soon change to a reddish color. They are laid on wheat heads, on the 

exposed tips of corn ears in the field, or on stored grain.

Upon hatching, each larva crawls to a kernel of grain and often spins a small entrance cocoon to 

assist it in boring into the hard kernel. After entering the grain, it feeds on either the endosperm 

or the germ until fully grown. It then eats out a channel to the outside of the seed and makes a 

weakly fastened flap at the exit by cutting the shell one-half to three-fourths of the circumference 

of a circle. The larva then spins a silken cocoon and changes to a reddish-brown pupa. Later, as 

a moth, it pushes its way through the flap. The period from egg to adult may be completed in 5 

weeks, although development is usually slower.

Figure 10. Ear of corn showing heavy infestation by the Angoumois grain moth.Note that certain 

kernels have three emergence holes, and that many kernels have served as food for two larvae.

 

4

Lepidoptera, Gelechiidae.
Stored Grain Insect Reference September 2016

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Figure 11. Life cycle of the Angoumois grain moth on wheat

Female moth lays egg on grain kernel. The larva emerging from 

egg gnaws a hole, no larger than a pin prick, through which it 

enters the kernel.

Kernel cut showing entrance channel. Larva feeds 

and grows, enlarging cavity.

The full-grown larva is as long as kernel in 

which it has eaten out a large cavity.

The pupa is the stage between larva 

and adult moth.

The moth leaves kernel by 

round hole shown.
Stored Grain Insect Reference September 2016

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Pink Scavenger Caterpillar

The pink scavenger caterpillar, Sathrobrota rileyi (Walsingham),5 is the larva, or caterpillar, of a 

small moth. It is pink, with a pale-brown head and thoracic shield, and is about five-sixteenths of 

an inch long when fully grown (fig. 12C). The moth which develops from this larva is smaller than 

the Angoumois grain moth, with a wing expanse of slightly less than hail’ an inch (fig. 12B). The 

forewings are handed and moiled with yellow’, reddish brown. and black. The pale-gray hindwings 

are very slender and are edged with long fringes.

This insect is common in the South, where it causes considerable injury to corn, both in the field 

and in storage. Infestation begins in the field and continues alter the corn is placed in storage. 

Figure 13 shows corn damaged by feeding larvae. A reliable indication of the presence of this pest 

is the large amount of loosely webbed films that rills the interstices between the kernels or fills the 

cavities of partially eaten kernels.

The pearly white eggs are usually laid singly, occasionally in twos or threes. The pinkish larva 

feeds on the seed, husk and cob with equal relish. The pink scavenger caterpillar is seldom a 

serious pest or commercial shipments, but it is capable of serious injury to corn, particularly as it 

comes In maturity in the field or while in the crib on Southern farms.

Figure 12. Grain moths: Left, Angoumois grain moth adult; center, pink scavenger caterpillar adult; 

right, pink scavenger caterpillar larva.

 

5

Lepidoptera, Cosmopterigidae.

Widespread use of the combine harvester has reduced wheat damage by this moth to a minimum. 

However, in the southern portion of the commercial corn-growing area. it periodically causes 

heavy losses to stored corn. Figure 10 shows an ear of corn with the external evidence of a heavy 

attack by the Angoumois grain moth. Figure 11 shows the successive stages in the development 

of this insect in a kernel of wheat, from egg to adult. Figure 12A shows the adult moth.
Stored Grain Insect Reference September 2016

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European Grain Moth

The European grain moth. Nemapogon ,granella (Linnaeus),6 is a small moth about the site of the 

Angoumois grain moth and is creamy while and heavily mottled with brown (Fig. 14). The mottled 

appearance distinguishes it from the Angoumois grain moth. It infests Il kinds n grain• bath in the 

field and in storage. The larva feeds on the grain and webs the kernels together.

This moth is found throughout the Northern States but is not very abundant and cannot he 

compared with the Angoumois grain moth in destructiveness.

Figure 13. Cut ear of corn showing characteristic feeding and destruction by pink scavenger 

caterpillar larvae. larvae eat from one kernel to another and often sever kernels from cob. Larvae 

sometimes eat into cob and transform into pupae there. Pupae are about one-third as long as the 

kernels shown.

 

6

Lepidoptera, Tineidae

Figure 14. European grain moth adult. Adult has a wing expanse of about onehalf of an inch.
Stored Grain Insect Reference September 2016

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Figure 15. Rice moth adult: Left, dorsal view with wings spread; right, side view with wings folded 

to body. Adult has a wing spread of about one-half of an inch.

Rice Moth

The rice moth, Corcyra cephalonica (Stainton),7 has a wing expanse of about half an inch and 

is pale grayish brown or tawny (fig. 15). The larva somewhat resembles that of the Indian meal 

moth. When fully grown the larva is about half an inch long and varies in color from white to a dirty, 

slightly bluish gray with occasional tints of green (fig. 16).

Damage by this pest, as with all moth pests, is done by the larvae, which are rather general 

feeders. They attack such materials as rice, cocoa, chocolate, dried fruit, biscuits, and seeds. The 

larvae produce a dense webbing as they become fully grown. When feeding upon grains, they 

spin dense silken tubes and web the grain kernels into the walls of the tubes. The moths live 1 to 

2 weeks, and each female lays 100 to 200 eggs. In summer, the development period from egg to 

adult is about 6 weeks. The rice moth has not as yet become very widely spread in this country.

 

7

Lepidoptera, Pyralidae

Figure 16. Full grown larva of the rice moth. about one-half of an inch long.
Stored Grain Insect Reference September 2016

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FLOUR MOTHS

Among the flour moths are some of the commonest and most serious pests of grain products. 

They are designated as flour moths, not because they feed entirely upon flour or milled products, 

but because they seldom attack sound kernels. These insects prefer broken grains, grains injured 

by major grain pests, and more especially milled cereal products such as flour, breakfast foods, 

and meals. All three flour moths are commonly found in grain ware-houses, but the Indian meal 

moth and the meal moth are probably the most frequently reported. These two moths may, under 

exceptionally favorable conditions, become established in whole grain and other seeds and cause 

injury, especially by eating out the germ.

Indian Meal Moth

The Indian meal moth. Plodia interpuncte!!a (Hubner),7 is a rather handsome moth with a wing 

expanse of nearly three-fourths of an inch (figs. 17 and 18A). It is easily distinguished from other 

grain pests by the peculiar markings of its fore-wings, which are reddish brown with a copper 

luster on the outer two-thirds but whitish gray on the inner or body ends.

Each female moth lays 100 to 300 eggs. singly or in groups. on food material.. Within a few days, 

the eggs hatch and small whitish larvae. or caterpillars, emerge. These larvae feed upon grains. 

grain podium, dried fruits, nuts, and a rather wide variety of foodstuffs,

Figure 17. The Indian meal moth: A. Moth with wings spread; B. moth with wings folded as 

ordinarily seen when the moth is resting on some surface in the warehouse. the moth has a wing 

expanse of nearly three-fourths of an inch.

A B
Stored Grain Insect Reference September 2016

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When fully grown, the larva is about half an inch long and is dirty white, sometimes varying to 

greenish and pinkish hues (fig. 18B). The larva spins a silken cocoon and transforms into a lightbrown pupa, from which the adult moth develops and later emerges. During warm weather, the 

Indian meal moth may pass through the egg, larval, and pupal stages in 6 to 8 weeks.

The larva of the Indian meal moth spins a web as it becomes fully grown and leaves a silken 

thread behind wherever it crawls. This webbing is often dense enough to attract attention when 

sacks of cracked corn, meal, or corn in the ear (that has been previously injured by other pests) 

have become heavily infested (fig. 19).

Figure 18. Flour moths: Left, Indian meal moth adult; center, Indian meal moth larvae; right, 

almond moth adult.

Mediterranean Flour Moth

The Mediterranean flour moth. Anagasta kuehniela (Zeller),7 has a wingspread of slighlly less than 

1 inch. Its hindwings are a dirty white, and the forewings which alone show when the moth is not 

flying are a pale leaden gray with transverse, wavy, black markings (fig. 20A, B).

This flour moth is a native of Europe. It was first found in the United States in California in 1892. 

Since then, it has become widespread over the country and for many years was considered the 

most troublesome pest of flour mills. The larva spins silken thread wherever it goes and webs and 

mats together particles of food on which it is feeding. The matted flour sometimes slogs the

machinery in flour mills and causes milling operators to stop. In mills that have an annual 

fumigation, this insect is no longer a major problem. Although it prefers flour and meal. the 

Mediterranean flour moth attacks grain, bran, cereal products, and many other foodstuffs.

The female moth lays small white eggs in accumulations of flour, meal, or waste grain. Within a 

few days, a small larva emerges from each egg (fig. 20C). When fully grown, the larva is about 

half an inch long and is whitish or pinkish, with a few small black spots on the body. The full-grown 

larva spins a silken cocoon, in which the insect transforms into a reddish-brown pupa (fig. 20D). 

Later, the adult moth emerges from the pupa. During warm weather, the Mediterranean flour moth 

requires 8 to 9 weeks to pass through the egg larval, and pupal stages.
Stored Grain Insect Reference September 2016

Page 20

Three other insect species occasionally infest grain or cereal products. They are the almond moth 

Cadra cautella (Walker), the tobacco moth. Ephestia elutella (Hubner), and the raisin moth, Cadra 

figulilella (Gregson). Of the three, the almond moth is the most troublesome pest (fig. 18C). It 

is commonly found in seed stores and is a serious pest of rough rice and grain sorghum in the 

South.

Figure 19. Ear of corn with characteristic loose 

webbing left by larvae of Indian meal moth, This 

moth rarely attacks sound grain but often attacks 

grain already injured by other grain pests. as 

shown here. Webbing develops only when 

grains are not moved for some time.

Meal Moth

The meal moth, Pyralis farinalis Linnaeus,7

is brownish, somewhat larger than the Indian 

meal moth (though it varies in size), and 

usually has a wingspread of about 1 inch.

Figure 21C shows the characteristic markings 

or pattern of the forewings. They are light 

brown with dark-brown patches at the bases 

and tips, and each forewing has two wavy, 

transverse white lines.

The meal moth is widely distributed and, in 

the larval stage, is a general feeder upon 

cereals, cereal products, hay, and many types 

of dried vegetable matter. It is usually found 

in damp basements or in other places where 

accumulations of damp, spoiled grain, bran, 

or meal are found. Though it prefers material 

that is damp and in poor condition, the meal 

moth may attack and severely damage sound 

wheat or cereal products, if these materials 

are stored in moist places or have a relatively 

high moisture content.

Meal moth larvae sometimes attract much 

attention because of their capacity to “webup” and bind together seeds of various kinds. 

The larvae cut through burlap sacks and can 

damage them greatly when heavy infestations 

develop in the sacked material. Figure 22 

shows the characteristic “webbing together” of 

infested seeds (in this instance navy beans). 

Figure 23 shows the tendency of the larvae 

to spin their whitish silken cocoons on the 

outside of grain sacks where the sacks touch 

one another. When the larvae cut sacks, the 

seeds fall out and lodge where the sacks 

touch. In such places, the seeds are usually 

heavily infested.
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The meal moth larva is whitish, and, when fully grown, is about 1 inch long (fig. 21B). The larva 

shows a contrast between the black of the head and the first body segment and the white of the 

remainder of the body. The body of the larva is often tinged with orange toward each end.

The larvae spin peculiar tubes of silk that contain mixed particles of food material. They rest in 

these tubes, which are very tough, and feed from the openings at the ends. When fully grown, the 

larvae leave the tubes, spin silken cocoons (also often covered with food particles), and transform 

into pupae (fig. 21A) from which the adult moths later emerge. The female moth lives about 1 

week and lays 200 to 400 eggs. In summer. the period from egg to adult is 6 to 8 weeks.

Figure 20. Mediterranean flour moth: A, adult (dorsal view) with wings spread: B. adult (side view) 

in resting position; C. larva: D. pupa (enlarged); E. abdominal joint of larva (enlarged). Adult moth 

has a wing expanse of slightly less than 1 inch.

C D E B

A
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Figure 21. Meal moth: A. pupa and (above) webbed grain mass with portion of pupa protruding: B. 

two well-grown larvae and (right) smaller larva: C. two adult moths. Markings on forewings easily 

distinguish this insect from other grain pests. Magnified about one and one-half times.

A B C

Figure 22. Navy beans, webbed together by meal moth larvae, adhere to sack.
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GRAIN AND FLOUR BEETLES

Cadelle

The cadelle, Tenebroides rnauritanicus (Linnaeus).8 is an elongate, oblong, flattened, black or 

blackish beetle about one-third of an inch long (fig. 24). It is sometimes called the bolting-cloth 

beetle because of its habit of cutting the silk cloths of bolting reels and redressing machines in 

flour mills.

The cadelle larva is one of the largest of the grain-infesting insects and is easily recognized. It 

is about three-fourths of an inch long, fleshy, with the abdomen terminating into two dark horny 

points (fig. 24B). The larva body is a dirty or chalky white, and the head, thoracic shield, and two 

horny points are black.

This insect is widespread over the world and is frequently found in mills, granaries, and 

storehouses, where it infests flour, meal, and grain. Both the larva and adult feed on grain and 

have the destructive habit of going from kernel to kernel devouring the germs. The cadelle is one 

of the longest lived of the insects that attack stored grain: many of the adults live for more than 1 

year and some of them for nearly 2 years.

 

8

Colcoptera. Trogositidae

Figure 23. Whitish cocoons spun by meal moth larvae on side of sack previously tilled with 

infested seed. Note dark pupae within cocoons, vetch seed webbed to sack by larvae. and 

(center) adult moth.
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The female beetle oviposits most of her life and, under las oralsk con-ditions, lays about 1000 

eggs.

The female lays cIusters of white nip III food material, Which hatch in 7 to 10 days in warm 

weather.

The larvae complete their growth in 2 to 14 months and then seek some secluded place in 

which to transform into the pupal stage They frequently bore into the timbers of the bin or other 

receptacle that holds the infested material, Roth the larvae and adults can live for long periods 

without food and often remain hidden in the woodwork of the bin for it long time after the grain has 

been removed. When new grain is put into the bin. it becomes infested in a surprisingly short time.

Figure 24. Cadelle: Left, adult, about one-third of an inch long: right, larva, about three-fourths of 

an inch long.
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Sawtoothed Grain Beetle 

The sawtoothed grain beetle. Oryzaephilus surinamenis (Linnaeus),9 is one of the best known of 

the cosmopoitan grain pests. It is a slender, flat, brown beetle about one-tenth of an inch long. It 

gains its name from the peculiar structure of the thorax, which bears six sawtoothlike projections 

on each side (fig. 25). It attacks, in both the larval and adult stages, all food of vegetable origin, 

especially grain and grain products such as flours, meals, breakfast foods, stock and poultry 

feeds, copra, nut meats, candies, and dried fruits,

The adults live, on an average. 6 to 10 months, but 

some adults may live as long as 3 years. The female 

beetle lays 43 to 285. eggs. She drops them loosely 

among the foodstuff or tucks them into a crevice in a 

kernel of grain The small. slender, white eggs hatch in 

3 to 5 days.

The emerging larvae do not stay within a single grain 

but crawl about actively and feed. During summer, 

they become fully grown in about 2 weeks. The mature 

larvae then construct delicate cocoon-like coverings by 

joining together small grains or fragments of foodstuffs 

with. a sticky secretion. Within these cells, the larvae 

change to the pupal stage, which lasts about 1 week. 

In summer, the developmental period from egg to Adult 

is 4 weeks.

Merchant Grain Beetle

A related species, the merchant grain beetle, 

Oryzaephilus mecator (Fauvell),7 is often confused with 

the sawtoothed grain beetle. It is less commonly found 

in grain than the sawtoothed grain beetle and appears 

to prefer oilseed products, including nuts. Cereal 

products are more to be infested with this insect than 

the gram itself.

In the merchant grain beetle, the eye diameter iv larger 

than the temple region behind the eve, and the head 

is rectangular A comparison with the smaller eyes and 

more triangular head of the sawtoothed grain beetle 

may he made frorn figure 26. The merchant grain 

beetle is also slightly larger and is a darker brown 

than the sawtoothed grain beetle. The habits and 

development of the two species are similar, but the 

merchant grain beetle lays only one-half to two-thirds 

as many eggs.

 

9

Coleoptera, Cucujidae

Figure 25. Sawtoothed grain beetle 

adult, about one-tenth of an inch 

long.
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Squarenecked Grain Beetle

Figure 26. Anterior comparison of sawtoothed and merchant grain beetles: Left, sawtoothed grain 

beetle adult; right, merchant grain beetle adult.

The squarenecked grain beetle, Cathartus 

quadricollis (Guerin-Meneville),9 is closely related 

to the sawtoothed grain beetle, which it ready 

resembles in form, size, and color. It is a flattened. 

oblong. polished, reddish-brown beetle about onetenth of an inch long. It differs from the sawtoothed 

grain beetle by its almost square thorax, which lacks 

the sawtoothlike projections (fig. 27).

This beetle is mainly abundant in the South, where 

it is found outdoors in great numbers in the seed 

pods of a great variety of plants. It is one of the 

most common beetles in stored corn in the South 

and, in the corn fields, is always found on damaged 

or exposed ears.

The immature stages closely resemble those of the 

sawtoothed grain beetles in both form and habit. 

The larvae have the bad habit of devouring the 

germs of the seeds in which they breed. These 

insects develop from egg to adult in about 3 weeks.

Figure 27. Squarenecked grain beetle 

adult, about one-tenth of an inch long.
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Foreign Grain Beetle

The foreign grain beetle, Ahasverus advena (Waltl),9 is a small reddish-brown beetle somewhat 

similar in appearance to the closely related squarenecked grain beetle, but is shorter and stouter 

(fig. 28).

Though of worldwide distribution, it is not important as an enemy of stored grains. It is attracted to 

damp and moldy grains, where it feeds on the molds. This insect is rarely found in clean grain.

Figure 28. Foreign grain beetle adult.

Mexican Grain Beetle

The Mexican grain beetle, Pharaxonotha kirschi Reitter,10 is a highly polished, deep-brown beetle 

about three-sixteenths of an inch long. It somewhat resembles the con-fused flour beetle in 

general appearance but can be readily distinguished from that insect by its more polished surface 

and longer antennae (fig. 29A).

This insect is common in Mexico and Guatemala, where it breeds in grain and grain products, but 

it is not known to be established in the United States.

 

10Coleoptera, Languriidae.
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Siamese Grain Beetle

The Siamese grain beetle, Lophocateres pusillus (Klug),8 is a flattened reddish-brown beetle 

slightly less than one-eighth of an inch long. It is characterized by the much flattened margins of 

the thorax and wing covers (fig. 30A).

This insect first appeared in this country in exhibits of rice and cereal from Siam, Liberia, and 

Ceylon at the Columbian Exposition, and it is now well established in the Southern States. It is 

commonly found in rice mills in Texas but does not cause serious damage.

Figure 29. Mexican grain beetle: A, adult; B, larva; C, pupa; D, leg of larva; E. antenna of larva. A, 

B, and C enlarged about 8 times; D and E greatly enlarged.

A

B

C

D E
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Flat Grain Beetle

Figure 30. Siamese grain beetle: A, adult; B, antenna of adult; C, larva; D, pupa enlarged.

A

B

C D

The flat grain beetle, Cryptolestes pusillus

(Schoenherr),9 is one of the smallest beetles 

commonly found in stored grain. It is a minute, 

flattened, oblong, reddish-brown beetle about 

one-sixteenth of an inch long, with elongate 

antennae about two-thirds as long as the body 

(fig. 31). It is cosmopolitan and is one the 

the commonest insect pests of stored grain. 

However, this insect is not a primary pest of 

stored grain, and the adult is apparently unable 

to survive in sound, uninjured grain. It follows 

up the attack of the more vigorous grain pests 

and is frequently found in enormous numbers 

with the rice weevil. This insect is a scavenger 

and often infests grain and meal that are in poor 

condition.

Figure 31. Flat grain beetle adult, showing 

characteristic long antennae. Body is not 

more than one-sixteenth of an inch long.
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The females deposit small white eggs in crevices in the grain or drop them loosely upon 

farinaceous mate-rial. The larvae are particularly fond of the wheat germ, and, in infested grain, 

many kernels are found uninjured except for the removal of the germ. The larvae also feed on 

dead insects. When fully grown, the larvae form cocoons of a gelatinous sub-stance to which 

food particles adhere. They transform into the pupal stage in these cocoons and later emerge as 

adults. Under favorable conditions, this insect may develop from egg to adult in about 5 weeks, 

but the average period of development in summer is about 9 weeks.

A related beetle, C. turcicus (Grouvelle), resembles the flat grain beetle so closely in appearance 

and habit that it is usually confused with that insect. This beetle, also, is cosmopolitan and the 

females of the two species are so similar that it is almost impossible to distinguish between them. 

The males, however, can be distinguished from each other by the length of the antennae. The 

antennae of the C. turcicus male beetle are as long as, or longer, than the body, but the antennae 

of the flat grain beetle male are only two-thirds as long as the body.

Rusty Grain Beetle

A third species, the rusty grain beetle, Cryptolestes 

ferrugineus (Stephens),9 is similar to the flat grain beetle 

and C. turcicus beetle in appearance and habit, but 

differs from them in the antennae (fig. 32) of the male 

beetle, which are not more than half as long as the body. 

This species is more resistant to cold weather than the 

other two species and is more commonly found in stored 

grain in the Northern States.

Confused Flour Beetle

The confused flour beetle, Tribolium confusum Jacquelin 

du Val,11 is a shiny, flattened, oval, reddish-brown beetle 

about one-seventh of an inch long. The head and upper 

parts of the thorax are densely covered with minute 

punctures. The wing covers are ridged lengthwise 

and are sparsely punctured between the ridges (fig. 

33). This insect is distributed over the world and is 

very abundant throughout this country. It is a general 

feeder on farinaceous material and Is undoubtedly the 

most abundant and injurious insect pest of flour mills 

in the United States. It ts found in granaries, mills, 

warehouses. and wherever grain or grain products are 

stored.

 

11Coleoptera, Tenebrionidae.

Figure 32. Rusty grain beetle adult.
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The average life of these beetles is about I year, 

but some have been known to live as long as 

3 years 9 months. The female lays an average 

of about 450 eggs. which are small and white, 

loosely in flour or other food material tn which 

the adults live. They are covered with a sticky 

secretion, thus becoming covered with flour or 

meal, and readilv adhere to she sides of sacks, 

boxes, and other containers. Consequently, 

fresh material placed in the containers is rapidly 

infested. The 1 eggs hatch in 5 to 12 days and 

small, wiry, slender, cylindrical, wormlike larvae 

emerge. When fully grown. they are about 

three-sixteenths of an inch long and are white 

tinged with yellow. These larvae feed on flour or 

other material

such as grain dust and the broken surfaces of 

grain kernels.

When fully grown, the larvae transform into 

small naked pupae. At first white in color, the 

pupae gradually change to yellow and then to 

brown and, shortly afterwards, transform into 

adult beetles. In summer, the period from egg to 

adult averages about 6 weeks under favorable 

weather conditions, but the life cycle is greatly 

prolonged by cold weather, as is true of all grain 

pests. Figure 33. Confused flour beetle adult.

Red Flour Beetle

The red flour beetle. Tribolium castaneum (Herbst),11 is almost identical in appearance to the 

closely related confused flour beetle. It can be distinguished from the confused flour beetle only 

with the aid of a magnifying glass. The segments of the confused flout beetle antennae gradually 

increase in size from the bases to the tips whereas the last few segments of the red flour beetle 

antennae are abruptly much larger than the other segments, forming enlarged tips. The head 

margins of the confused flour beetle are expanded and notched at the eyes, with a ridge over the 

eye. The pronotum is widest at the anterior third. The head margins of the red flour beetle are 

nearly continuous at the eyes and do riot have a ridge over the eye. The pronotum is widest at the 

middle. The differences between the two species are shown in figure 34.

This insect is constantly associated with the confused flour beetle and has similar feeding and 

breeding habits. the immature stages of the two insects are so similar that it is impossible to 

distinguish between them. The developmental period from egg to adult is usually somewhat 

shorter than for the confused flour beetle. Although it is cosmopolitan, the red flour beetle is found 

most commonly in the Southern United States, where it causes very serious damage to grain 

products. 
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In addition to the damage it causes by feeding, this insect imparts a nauseous smell and taste 

to the material it infests. Like the confused flour beetle, the red flour beetle is primarily a pest of 

milled products. It is present in grain shipments, where it attacks only grain dust and the surfaces 

of broken grains; hence, it is not a primary pest of commercial shipments.

Figure 34. Anterior comparison of confusum (confused) and castaneum (red) flour beetles: Left, 

confusum (confused) flour beetle adult; right, castaneum (red) flour beetle adult.

American Black Flour Beetle

The American black flour beetle Tribolium audax Halstead,11 is found as commonly outdoors as 

it is in storehouses. Until recently, it was confused with the European T. madens (Charpentier), 

which it resembles in appearance and habits (fig. 35A). Although not so well known as the 

contused and red flour beetles, it has similar habits, and is occaisionally found infesting grain and 

grain products in flour mills and storehouses.

This insect is seldom found in injurious numbers and is by no means as widespread as T. 

confusum and T. castaneum. It occurs in its greatest abundance in the Rocky Mountain States, but 

it has been reported from widely scattered points over the country. It may be readily, distinguished 

from the confused and red flour beetles by its black color and larger size. This insect is about onesixth of an inch long. Infestation of poultry feed by T. destructor

Uyttenboogaart, another species of this destructive group of flour beetles. was recently reported 

from Montreal. Canada. It was introduced from Europe.
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Figure 35. Flour beetles: A, American black flour beetle adult; B. longheaded flour beetle adult; C, 

slenderhorned flour beetle adult; D, smalleyed flour beetle adult; E, depressed flour beetle adult.

A

C D E

B
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Longheaded Flour Beetle

The longheaded flour beetle, Latheticus oryzae Waterhouse,11 is a slender. flattened beetle slightly 

less than one-eighth of an inch long. It is somewhat similar in form to the confused flour beetle 

but is narrower and is pale yellowish brown (fig. 35B). The beetle is further differentiated from the 

confused flour beetle by the peculiarly shaped antennae and the minute canthus behind each eye.

The longheaded flour beetle has been reported from most parts of the world as having infested 

wheat, rice, corn, barley, rye, flour, and similar products. It was first recognized in this country from 

specimens collected in Texas in 1908 and is now wide-spread in the Southern and Middle Western 

States, where it is common in rice and flour mills. This beetle infests grain and grain products in 

the mills and causes the same type of damage as that done by the confused flour beetle.

Slenderhorned Flour Beetle

The slenderhorned flour beetle, Gnatocerus maxillosus (Fabricius),11 is closely related to the 

broadhorned flour beetle and is of similar form and appearance (fig. 35C). It is about one-eighth of 

an inch long. In addition to its smaller size, this insect may be distinguished from the broadhorned 

flour beetle by the slender incurved “horns” with which mandibles or jaws of the male are armed. 

Its habits are similar to those of the broadhorned flour beetle, but it is less common in the United 

States and is more or less confined to the Southern States.

Smalleyed Flour Beetle

The smalleyed flour beetle, Palorus ratzeburgi (Wissmann),11 is the smallest of the flour beetles 

that infest grain and grain products in this country. It is tiny, somewhat oblong, flattened, shiny, 

reddish-brown beetle about one-tenth of an inch long (fig. 35D). This insect occurs throughout 

the world and is widely distributed in this country. It breeds in grain and milled products and is 

frequently found in flour-mill basements.

Depressed Flour Beetle 

The depressed flour beetle, Palorus subdepressus (Wollaston),11 is similar in appearance and 

habits to the smalleyed flour beetle. It is slightly larger than that species, and the sides of the 

front of the head are strongly reflexed and extend back-ward to conceal the front portions of the 

eyes (fig. 35E). In the smalleyed flour beetle, the sides of the front do not extend backward. The 

depressed flour beetle, also, is cosmopolitan but is much less common in the United States than 

the smalleyed flour beetle, except perhaps in the Great Plains.
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Broadhorned Flour Beetle

The broadhorned flour beetle, Gnatocerus cornutus (Fabricius),11 owes its name to the peculiar 

structure of the mandibles, or jaws, of the male beetle, which are armed with a pair of broad, 

stout “horns.” It is a stout, reddish-brown beetle about one-sixth of an inch long, and it closely 

resembles the other flour beetles in appearance but is easily distinguished from them by the 

peculiar structure of its jaws (fig. 36). It is cosmopolitan and is common in all parts of the United 

States, except in the Great Plains, where it is comparatively rare. This insect prefers to feed in 

flour and meal but is found in a variety of grains. The adult beetles frequently live for 1 year or 

longer. The female lays 100 to 200 small white eggs which hatch in 4 to 6 days in warm weather. 

The development period from egg to adult is 6 to 8 weeks.

Figure 36. Broadhorned flour beetle: Left. larva; center, pupa; right, adult. Adult is about one- sixth 

of an inch long,
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Larger Black Flour Beetle

The larger black flour beetle, Cynaeus angustus (LeConte),12 described in 1852, was little known 

as a pest of stored grain and grain products until 1939, when it was found in a flour mill in Seattle, 

in stored wheat in Kansas, and in stored corn in Iowa.

It is now fairly common in farm-stored grain in the North Central States. It is a stout, reddish-brown 

or black beetle about one-fourth of an inch long (fig. 37). This insect is known to live for 6 months 

and may live for at least 1 year under favororable conditions. The life cycle from egg to adult can 

be completed in 4 weeks, but it usually requires 6 to 10 weeks. This insect prefers grain that is 

high in moisture.

Figure 37. Larger black flour beetle adult, about one-fourth of an inch long.

 

12Coleoptera, Dermestidae.
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EGGS OF FLOUR AND GRAIN INSECTS

The eggs of the common flour and grain-infesting insects are rarely seen by the layman. They 

are usually white and are often covered with a sticky substance that causes particles of flour or 

other material to adhere to them, thus making them difficult to distinguish from the foodstuff in 

which they are deposited. Some eggs arr oval or oblong-oval, and others are slender and spindle 

shaped. Their small size is well illustrated in figure 38, which shows the eggs of four different 

species of insects on a piece of 10XX silk bolting cloth. The eggs of the flat grain beetle are so 

small that if placed side by side, they would average about 150 per inch. Those of the cadelle, 

which is one of the larger beetles that infests stored cereal products, if placed end to end, would 

average about 19 eggs per inch. During the process of milling flour and preparing it for the market, 

the flour is sifted through silk bolting cloth to remove insect eggs and other impurities. 

Figure 38. Eggs of flour and grain insects: A, Broadhorned flour beetle; B, cadelle; C. 

Mediterranean flour moth; D, confused flour beetle. Photo greatly enlarged.

A

B

C

D
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MEALWORMS

The term “mealworm” applies to the larvae of several beetles of the family Tenebrionidae that are 

nocturnal and frequent dark places. They breed in refuse grain, coarse cereal, and mill products 

that accumulate in dark corners, under sacks, in bins, and in similar places. They inhabit moist 

places and are often found among slightly damp bags.

Yellow Mealworm

The yellow mealworm, Tenebrio molitor Linnaeus,11 is one of the largest insects that infest stored 

cereal products. This insect is cosmopolitan; in the United States, it is abundant only in the 

Northern States.

The adult is a polished dark-brown or black beetle somewhat more than half an inch long (fig. 

39A). Its thorax is finely punctured, and its wing covers are longitudinally striated or grooved. The 

female lays bean-shaped white eggs covered with a sticky secretion that causes the flour, meal, 

or grain waste in which they are placed to adhere to them. The eggs hatch in about 2 weeks and 

slender white larvae emerge. The larvae soon turn yellow and assume the form shown in figure 

39C. When fully grown, the larvae are about 1 inch long and are yellowish, shading to yellowish 

brown toward each end and at the articulation of each segment. The yellow mealworm gets its 

name from the yellowish color of the larvae.

There is but one generation each year. The adults begin to appear in the latitude of Washington, 

D.C., in late May and early June and may be ,found until late in August. The female beetles are 

quite prolific, and each may lay as many as 500 eggs. The larvae become fully grown in about 3 

months, but, instead of trans-forming into the pupal and adult stages, they continue to feed and 

molt until cold weather and then hibernate. Later on, in late spring or early summer, they transform 

into the pupal stage for about 2 weeks.

Because the yellow mealworm has but one generation each year and is entirely an external 

feeder upon grains, it is not a serious pest. Screening and fanning will easily remove it from grain 

shipments. The well-grown larva, however, can do serious injury to whole grains under certain 

conditions, when grain is held for long periods without being moved.
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Figure 39. Mealworms: A, yellow meal worm adult; B, dark mealworm adult; C, yellwo mealworm 

larvae; D, dark mealworm larvae.

A B

C D
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Dark Mealworm

The dark mealworm, Tenebrio obscurus Fabricius,11 is very similar in form, size, and color to the 

closely related yellow mealworm. However, the adult is a dull, pitch-black beetle, in contrast to the 

shiny or polished dark-brown or black yellow meal-worm adult (fig. 39B). The dark mealworm larva 

so closely resembles the yellow mealworm larva that it can best be distinguished from that species 

by its much darker color (fig. 39D).

These two species are often found together since they have similar feeding habits. The 

overwintering larvae of the dark mealworm begin to pupate earlier than those of the yellow 

mealworms, and, in the Washington, D.C., area the adult beetles emerge during April and May.

Lesser Mealworm

The lesser mealworm, Alphitobius diaperinus (Panzer),11 resembles the yellow and dark 

mealworms in form and color but is considerably smaller. It is black or very dark reddish brown 

and is three-sixteenths to four-sixteenths of an inch long (fig. 40A). The larva is yellowish brown 

and closely resembles the young larva of the yellow mealworm in form and appearance (fig. 40B). 

This insect is cosmopolitan and is commonly found in flour-mill basements in damp or musty flour 

or grain. It prefers grain and cereal products that are slightly out of condition and is commonly 

associated with poultry feed.

Figure 40. Lesser mealworm: Left, adult; right, larvae.
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Black Fungus Beetle

The black fungus beetle, AIphitobius laevigatus (Fabricius),11 is almost identical in appearance 

to the lesser mealworm and has similar habits. It prefers damp, moldy grain and cereal products 

End does not cause serious damage to sound grain. This insect may be distinguished from the 

lesser mealworm by the curved sides of the thorax. which are coarsely and densely punctuated on 

the surfaces, whereas. in the lesser mealworm. the sides are nearly straight and the surfaces are 

Finely and sparsly punctured (fig. 41C). In the United States, the black fungus beetle is much less 

abundant than the lesser mealworm.

Figure 41. Black fungus beetle: A, larva; B, pupa; C, adult; D, caudal segment of larva: E, lateral 

plate of pupa. Larva is about 1 inch long.

A

B C

D E

Redhorned Grain Beetle

The redhorned grain beetle, Platydema 

ruficorne (Sturm),11 is a broadly oval beetle 

slightly less than one-fourth of an inch long. It 

is velvetv black with a purplish tinge and has 

reddish-yellow antennae (fig. 42). Reported to 

be common on fleshy fungi and underneath 

tree bark, it was found in abundance in shelled 

corn in Missouri in 1940 and was also found in 

shelled corn in Illinois and Iowa. This insect is 

particularly attracted to damp and moldy grain.

Figure 42. Redhorned grain beetle adult, 

about one-fourth of an inch long.
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DERMESTID BEETLES

In general, the dermestids are a group of beetles that scavenge and feed on animal matter. 

Certain species, however, belonging to the genera Trogoderma, Amhrenus, and Attagenus, vary 

their diet by feeding on farinaceous materials. They are frequently present in flour mills, farm 

granaries, warehouses, and similar places where grain) and grain products are stored.

Black Carpet Beetle

The black carpet beetle, Attagenus megatoma (Fabricius),12 is a small, oval beetle two-sixteenths 

to three-sixteenths of air inch long (fig. 43A). The head and thorax are black, but the wing covers 

are black or dark-reddish brown and are covered with short hairs. Its legs and antennae are 

dark yellow.. The larva is very characteristic and can be easily recognized. It is reddish or golden 

brown, is covered with short, scalelike, appressed hairs, and has a tuft of long hairs at the end of 

the body (fig. 44).

The larvae are often found in abundance in cracks is the floors of warehouses where foodstuffs 

have accumulated. In the spring, these larvae transform into adults, which swarm over bagged 

material stored there. Because the larvae of the black carpet beetle develop slowly, there is only 

one generation each year. If conditions are unfavorable, the life cycle may be prolonged to 2 or 

3 years. The adults, which emerge in the spring and early summer, live 2 to 4 weeks, and each 

female lays; about 100 eggs. This beetle is cosmopolitan.

Trogoderma Beetles12

The best known member of this group is Trogoderma inclusum LeConte,12 which is a common 

pest of grain, seed, and other stored products in the Great Plains States. The adult beetle is onefourteenth to one-sixth of an inch long. The female is about 1-1/3 times the size of the male. The 

beetle is reddish brown to black with indistinct pater markings on the wing covers.

The larva is stout, and, at rest, the back is yellowish brown (fig. 45). However, the areas between 

the segments, which are visible during movement, and the underside are very pale yellow. The 

last three segments of the body are almost covered by tufts of dense, specialized hairs. The fully 

grown larva may attain a length of one-fourth of an inch. This insect larva is difficult to distinguish 

from the larvae of related species.

The adult female beetle lays up to 96 eggs. The life cycle varies from 7 weeks to several years, 

depending upon the temperature and the food supply.

Trogoderma glabrum (Herbst) is very similar to T. inclusum and is found in similar situations. The 

adult lacks the longitudinal pale markings on the midportion of the wing covers, and differences in 

the eyes and antennae of the two species can normally be determined only in the laboratory (fig. 

43B). The larvae are also very similar, but T. glabrum larvae are generally darker, or more reddish 

brown than yellowish brown.

The so-called warehouse beetle. Trogoderrna variabile BaIlion (T. parabile Beal), is widespread 

but difficult to recognize because of its variable appearance.
Stored Grain Insect Reference September 2016

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Figure 43. Dermestid Beetles: A, black carpet beetle adult female; B Trogoderma glabrum (H.) 

adult; C, varied carpet beetle adult; D, khapra beetle adult. (Drawing of khapra beetle adult 

courtesy of California Department of Agriculture.)

A B

C D
Stored Grain Insect Reference September 2016

Page 44

Figure 44. Larva of black carpet beetle (with tuft 

of hairs), about two-fifths of an inch long.

Figure 45. Larva of Trogoderma inclusum LeC.
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Page 45

Worldwide, the khapra beetle, Trogoderma granarium Everts, is the most destructive of this group 

(fig. 43D). It was discovered in Tulare County. Calif., in 1953 and is thought to have been present 

in the San Joaquin Valley since 1939.

Before its discovery, this insect had spread to other points in California and into Arizona, New 

Mexico, Texas, and Baja California, Mexico. A Federal quarantine was invoked in February 1955 

to deter the spread of this pest to other areas, and an eradication program was started. By 1961, 

active infestations were eliminated, and strict quarantine measures have kept the beetle from 

becoming reestablished in the United States.

This beetle prefers dried vegetable matter to animal matter as food but will attack almost any kind 

of either material. Grain damaged by the khapra beetle has somewhat the same appearance as 

grain attacked by the lesser grain borer.

Under favorable conditions, the khapra beetle breeds so rapidly that the larvae often appear in 

large numbers in the surface layers of binned grain. The larvae crowd into the crevices of building, 

bins, and so forth, and are difficult to reach with insecticides. Since this beetle has limited mobility, 

it spreads principally through the agency of man.

Other species of Trogoderma in this country that may be confused with those mentioned here are 

T. grassmani Beal, T. ornatum (Say), T simplex Jayne, and T. sternale Jayne. All these species 

are sometimes confused with the Anthrenus species, which are not grain pests. The varied carpet 

beetle, A. verbasci (Linnaeus), however, has been found in mills and storage facilities (fig. 43C).
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SPIDER BEETLES13

Several species of beetles belonging to the family Ptinidae are occasionally found infesting grain 

and cereal products. They attract attention by their peculiar, spiderlike form. These insects are 

rather wide-spread in distribution but are rarely abundant enough in the United States to cause 

serious damage.

Figure 46. Hairy spider beetle adult. about 

one-seventh of an inch long.

Hairy Spider Beetle

The hairy spider beetle Ptinus villiger (Reitter),13

is a reddish-brown beetle marked with four 

irregular white patches. It is about one-seventh 

of an inch long (fig. 46). This insect is a rather 

common pest in the Prairie Provinces of Canada 

and is occasionally destructive in the adjoining 

Northern United States. It attacks stored grain 

and all types of ground-cereal products. The adult 

beetle appears in warehouses in the spring and 

lays eggs in flour, feed, or other cereal products. 

The female lays about 40 eggs. Under favorable 

conditions, the development period from egg to 

adult is about 3-1/2 months. The full-grown larvae 

construct characteristic silken pupal cases, which 

are covered with food particles from the food 

material in which they occur. An allied species, P. 

raptor Sturm, is about as common in Canada as 

the hairy spider beetle.

Whitemarked Spider Beetle

The whitemarked spider beetle, Ptinus fur

(Linnaeus), is also found in the Northern States 

and is somewhat more abundant than the hairy 

spider beetle, which it closely, resembles in 

appearance and habits (fig. 47). It feeds on both 

animal and plant matter and attacks flour, feed, 

grain. and miscellaneous foodstuffs. It is rarely 

abundant enough to cause serious damage.

 

13Coleoptera, Ptinidae.

Figure 47. Whitemarked spider beetle adult 

female. The elongate-oval male is not so 

conspicuously marked as the female.
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Brown Spider Beetle

The brown spider beetle. Primus (*wipes (Panzer). closely resembles the whitemarked spider 

beetle in size. color. general appearance. and habits. It may be distinguished from that beetle by 

the absence of white markings on the wing covers.

Figure 48. American spider beetle adult, image 

enlarged.

Other Spider Beetles

The Australian spider beetle, Ptinus ocellus

Brown, has been reported from the United 

States but is rarely found here. It is very similar 

in general appearance and habits to the brown 

spider beetle.

The American spider beetle, Mezium 

americanum (Laporte), is a small spider 

beetle of striking appearance. It has a shiny, 

subglobular body that distinguishes it from 

the preceding spider beetles (fig. 48). It is 

somewhat of a scavenger and feeds on dried 

animal products and plant matter. It is not 

an important pest of stored grain or grain 

products. but it is occasionally found in mills, 

‘warehouses, and dwellings.

A closely related species, Gibbium psylloides

(Czenpinski), resembles the American spider 

beetle in appearance and habits and is found 

in similar situations. It may be distinguished 

from that insect by the head and thorax. which 

are densely covered with small scales and 

scalelike hairs. This species States, whereas 

M. affine (Boieldieu) reportedly occurs only 

in the extreme is the common form in the 

Northern southern portion of the United States 

and Canada.
Stored Grain Insect Reference September 2016

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MISCELLANEOUS BEETLES

Twobanded Fungus Beetle

The twobanded fungus beetle, Alphitophagus 

bifasciatus (Say),11 is a handsome, elongateoval beetle slightly less than one-eighth of an 

inch long. It is reddish brown with two broad 

black bands across the wing covers (fig. 49). 

This insect is distributed over the world and. as 

a scavenger, generally feeds on such materials 

as fungi and molds in refuse grain and grain 

products, and decaying vegetable matter. It is 

frequently found around mills and storehouses 

where waste material is allowed to accumulate 

and in wet or damaged grain in the holds of 

grain ships. The larvae have been reared in 

moist cornmeal and in spoiled cereals.

Hairy Fungus Beetle

The hairy fungus beetle, Typhaea stercorea 

(Linnaeus),14 is frequently’ found in cornfields, 

where it is apparently attracted to the decaying 

kernels of exposed ears. After corn is harvested 

and shelled, it is often heavily infested by this 

insect, but there is little feeding on undamaged 

grain. This beetle is cosmopolitan and is found 

in all parts of the United States in dwellings. 

warehouses, stores, flour mills, granaries, and 

similar places.

It is a small brownish beetle about one-tenth of 

an inch long and is covered with hairs (fig. 50). 

It rather closely resembles the drugstore beetle 

in general appearance but is smaller (fig. 50A). 

This insect can also be easily distinguished 

from the drugstore beetle by the shape of 

its antennae, which are clavate instead of 

irregularly serrate.

 

14Coleoptera, Mycetophagidae.

Figure 49. Twobanded fungus beetle 

adult. Image enlarged about 20 times.

Figure 50. Hairy fungus beetle adult, 

about one-tenth of an inch long.
Stored Grain Insect Reference September 2016

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Corn Sap Beetle

The corn sap beetle, Carpophilus dimdiatus 

(fabricius),15 may be recognised byits peculiar 

wind covers, which are short and truncate, 

leaving the tip of the abdomen exposed. It is a 

small, oblong, ovoid, dark-brown beetle, with 

lighter colored wind covers and is one-tenth to 

one-eighth of an inch long (fig. 51).

This insect normally feeds in rotting or decaying 

fruit and other vegetative forms and in the 

sap exuding from injured plants. It is quite 

numerous in cornfields in the South, where it 

swarms over the damaged ears and feeds and 

breeds in the decaying kernels. The corn sap 

beetle is attracted to damp, decaying grain,and, 

not infrequently, it is found in rice mills breeding 

in accumulations of broken rice. It is often seen 

in swarms, crawling over bags of rice.

A closely related beetle, Carpophilus

(Urophorus) humeralis (F.), which was 

introduced from abroad, is becoming more and 

more abundant in this country. It is similar in 

form to the corn sap beetle but is slightly larger 

and is a uniform shiny, dark brown all over. Its 

habits are vary similar to those of the corn sap 

beetle.

Figure 51. Corn sap beetle adult. Image 

enlarged.

Cigarette Beetle 

The cigarette beetle, Lasioderma serrzcorne (Fabricius),16 is a small, stout, oval, reddish yellow 

or brownish-red beetle, with the head bent down nearly at a right angle to the body. This gives 

the beetle a humped appearance when viewed from the side, as shown in figure 52C. It varies in 

size, but is usually about one-tenth of an inch long. This insect, found in all temperate, subtropical 

regions, infests tobacco and many other stored products. It breeds in a variety of seeds and may 

occasionally be found attacking grains left in storage in the original sacks for long periods. 

The adult beetles live 2 to 4 weeks, and, during this time, each female may lay as many as 100 

eggs. The developmental period from egg to adult is quite variable but, under favorable conditions, 

is 6 to 8 weeks.

 

16Coleoptera, Anobiidae.
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Drugstore Beetle 

Tho drugstore beetle, Stegobium paniceum (Linnaeus),16 is very similar in appearance to the 

closely related cigarette beetle but is more elongate in proportion to width and has distinctly 

striated wing covers. The adult insect is about one-tenth of an inch long and has a cylindrical, 

uniformly light-brown body covered with a fine, silky pubescence (fig. 53A, B). The larva, or grub, 

is considerably less hairy than that of the cigarette or tobacco beetle (fig. 53C). It is known as the 

drugstore beetle from its habit of feeding on pharmaceutical drugs. This insect is a very general 

feeder that attacks a great variety of stored foods, seeds, and other materials, and it reportedly 

“eats anything except cast iron.” It is frequently found in storehouses and granaries around the 

world. 

This beetle lays eggs in almost any dry organic substance. The small white grubs emerge from the 

eggs and then tunnel through these substances. When fully grown, they pupate in small cocoons. 

The entire life cycle may be passed in less than 2 months. 

Catarama Beetles

Members of the genus Tricorynus,

16 formerly Catorama, are closely related to the drugstore and 

cigarette beetles. This group includes T. herbarius (Gorham), known as the Mexican book beetle, 

T. confusus (Fall), and T. tabaci (Guerin- Meneville). T. herbarius is about one- eighth of an inch 

long. T. confusus (fig. 54) is slightly smaller, and T. tabaci is slightly larger. These insects are only 

occasionally found in stored grain and do not cause serious damage. 

Figure 52. Cigarette beetle: Left, larva; center, adult (dorsal view); right, adult (side View). Adult is 

about one-tenth of an inch long.
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Page 51

Murmidius Beetle17

The minute beetle, Murmidius ovalis (Beck),17 is sometimes found in stored grain or cereal 

products. It is shiny, dark-reddish brown and is less than one-sixteenth of an inch long (fig 55). 

This lnsect lays sculptured eggs, which are fastened in place on their sides. The larvae, which 

are unusual in appearance, are pale yellow, oval in outline (with the head invisible from above), 

flattened, with bristly appendages around the margins and boathook-shaped setae on their back.

These insects pupate in a hemispherical cocoon, which is fastened down on its flat base. They 

require a high humidity and, under hot conditions, can complete development in less than 2 

months. Under cooler conditions; they may require more than 7 months for development. 

 

17Coleoptera, Cerylonidae.

Figure 53. Drugstore beetle: A, adult (dorsal View); B, adult (side view); C, larva. Adult is about 

one-tenth of an inch long. This insect attacks only undisturbed grain that has been in storage for 

long periods.
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Page 52

Figure 54. Catorama beetle (Tricorynus confusus (F.)) adult.

Figure 55. Murmidius beetle (Murmidius ovalis (B.)) adult.
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BOOKLICE OR PSOCIDS 

Grain and grain products are sometimes found to be swarming with minute insects scarcely larger 

than a pinhead. Flour and grain samples are particularly attractive to them. They are known as 

psocids, or booklice, owing to their resemblance to lice and their occasional presence in books. 

These insects belong to several closely related species of the genus Liposcelis.

18 They are tiny, 

pale gray or yellowish white, wingless, soft bodied, louselike insects with fairly large heads, poorly 

developed eyes, and long slender antennae (fig. 56). These insects are about one twenty-fifth of 

an inch long. They feed on a great variety of organic matter, both of plant and animal origin, but 

are troublesome through their presence alone, not because of the actual damage they cause.

Some females are believed to reproduce without mating, but males are sometimes found with 

them. Each female may lay as many as 100 eggs, and, in summer, the developmental period from 

egg to adult is about 3 weeks. The newly hatched young resemble the adults in form and general 

appearance but are smaller and lighter in color. These insects are widely distributed in North 

America and Europe.

A closely related species, the larger pale booklouse, Trogium pulsatorium (Linnaeus), known 

as “the death watch,” is similar in appearance and habits and is found under the same 

circumstances. It may be distinguished from the common book-louse by its slightly larger size, 

diminutive wing covers, and well-developed eyes. This insect, also, is widely distributed over North 

America and Europe but is not quite so common or abundant as the preceding species.

 

18Psoptera, Liposcelidae.

Figure 56. Book louse or psocid adult Enlarged.
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SILVERFISH

The silverfish or slicker, Lepisma saccharine Linneaus,19 is commonly found in mills, warehouses, 

and dwellings. It is a shiny, silver or pearl-gray insect with three long, tail-like appendages, 

which make it easy to recognize. It is cosmopolitan and feeds on starchy foods of all kinds. It is 

particularly found in dark, moist, warm situations.

A closely related species, the firebrat, Thermobia domestica (Packard), is found in similar 

situations and closely resembles the silverfish in appearance and habits (fig. 57). This insect may 

be differentiated from the silverfish by its broader body. It is pearly white and is heavily mottled 

along the back, with dusky scales that give it a banded appearance when some of the scales 

have rubbed off. It is cosmopolitan and, in some areas of the world, is more abundant than the 

silverfish. The developmental period from egg to adult is 11 to 12 weeks.

Figure 57. Firebrat adult, about 2-1/4 times 

natural size. 

19Thysanura, Lepismatidae.
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COCKROACHES20

The familiar cockroaches are frequently found in establishments that contain cereal products. 

They are particularly abundant in the basements of buildings in dark, moist situations, and, when 

lights are suddenly turned on, it is not uncommon to see the floors almost black with them. 

The oriental cockroach, Blatta orientalis Linnaeus, is probably the commonest species found in 

flour mills and food establishments in North America. It is a large, dark-brown or black roach, 

about 1 inch long at maturity (fig. 58). The females are unique because they have short wing pads 

but no functional wings (fig. 58A). The males have fully developed wings (fig. 58B).

A closely related species, the American cockroach, Periplaneta americana (Linnaeus), is 

also quite abundant and is the predominant form in many flour mills in the Southwestern and 

Midwestern States. It is larger than the oriental cockroach and frequently is 1-1/2 inches long. This 

insect is bright sienna brown, except for the brownish-yellow pronotum, which encloses the

characteristic, irregularly shaped, reddish-brown double spot in the center 

(fig. 59).

Figure 58. Oriental cockroach: A, adult female; B, adult male; C, adult female (side view); D, halfgrown cockroach. Enlarged.

A

B

C D

 

20Orthoptera, BIattidae.
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FLOUR OR GRAIN MITES21

The flour or grain mites are pale. grayish white, smooth. wingless, soft-bodied creatures. They are 

microscopic in sire and have numerous long hair on the legs and back (fig. 60). Mites are not true 

insects because the adults have eight legs and the body is indistinctly divided into two parts. The 

flour or grain mites, usually less than one-fiftieth of an inch long. are much smaller than the book 

lice.

They are often found in stored grain and occasionally increase in numbers so rapidly that the grain 

seems to be quite alive with them. During heavy infestations, their cast skins and dead bodies 

accumulate into fluffy, light-brown masses beneath the sacks of grain. If these accumulations are 

on a warehouse floor, they roll up into piles, which move about with each gust of wind. No other 

group of grain pests produces these masses. When present in large numbers. the flour or grain 

mites promote sweating, impart a disagreeable odor to the grain, and may cause damage by 

feeding.

 

21Acarina, Acandae.

Figure 59. American cockroach: Left. adult (dorsal view); right, adult (ventral view). Enlarged.
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Fortunately, the mites that attack grain are preyed upon by predaceous mites, which usually 

become abundant enough to kill the grain mites in a comparatively short time. If not, screening 

and fanning the grain will usually reduce grain mite infestations to a point where no injury occurs.

Acarus siro Linneaus, known as the flour mite, common forage mite, or grain mite, is the most 

injurious species of mite found in flour, grain, and cereal products in North America. It multiplies 

very rapidly under favorable conditions and may complete its life cycle, from egg to adult, in 

slightly over 2 weeks.

Species of the genus Tyrophagus and other related genera, also known as flour mites or cheese 

mites, are common in grain. They are similar in appearance and habits to A. siro.

Figure 60. Grain mites. Greatly enlarged.
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PARASITES OF GRAIN PESTS

Swarms of small wasplike insects, of the size and appearance shown in figure 61, are sometimes 

found in bulk grain. Similar insects may also be seen on the windows of flour mills and other 

establishments where cereal products are handled. These insects are not harmful to grain but are 

beneficial because they attack and destroy the insects that infest grain and grain products.

The small parasite shown resting on a kernel of wheat in figure 61 is the adult of Anisopteromalus 

calandrae (Howard),22 the most important parasite of the rice and granary weevils. The female 

wasp can detect the presence of the grain-weevil grub hidden from sight within the grain and 

paralyzes it with a few thrusts of the ovipositor. She then deposits one egg on the exterior of the 

grub or in close proximity to it. The egg hatches, and the parasite grub feeds on the paralyzed 

weevil grub and destroys it. The developmental period from egg to adult is about 2 weeks. One 

female parasite wasp is known to lay as many as 283 eggs, but the help usually comes too late 

to prevent damage to the crop. A related species, Choetospila elegans Westwood,22 is somewhat 

less commonly found as a parasite of the same insects.

 

22Hymenoptera, Pteromalidae.

Figure 61. Anisopteromalus calandrae (H.) adult, a hymenopterous parasite of grain pests, resting on 

a wheat kernel.
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Figure 62 shows another fairly common parasite of the grain beetles. This insect, Cephalonomia 

tarsalis (Ashmead),23 has habits quite similar to those of the preceding species.

Figure 62. Cephalonomia tarsalis (A.) adult. Enlarged.

Figure 63 shows the adult of Bracon hebetor Say,24 attacking flour moth larvae. This little wasp 

is one of the most important parasites of these moths. It first paralyzes the flour moth caterpillar 

by stinging it several times. It then deposits several eggs on the paralyzed caterpillar. These eggs 

hatch into small, white, footless, grublike larvae that suck the body juices of the caterpillar. Under 

favorable circumstances, this parasite develops from egg to adult wasp in less than 2 weeks.

The species Venturia canescens (Gravenhost),25 is even more important as a beneficial parasite 

of the flour and meal moths. This slender wasp has a reddish-brown abdomen, black head and 

thorax, and reddish-brown to yellow legs (fig. 64).

The habits of this parasite are somewhat different from all the above mentioned parasites of grain 

pests. The adult wasp deposits eggs inside the body of the flour moth caterpillar, and the entire 

development of the parasitic larvae, until just before pupation, takes place within the host. The 

host caterpillar is not paralyzed and continues feeding until the parasitic larva has become nearly 

full grown. The developmental period from egg to adult is 3 to 4 weeks.

Grain dealers and millers not infrequently find a small, threadlike, white worm, about three-fourths 

of an inch long, in accumulations of flour or grain dust (fig. 65). This worm is the larvae of a small black 

fly, Scenopinus fenestralis (L.) 26 known as the windowpane fly because it frequents the windows 

of mills and similar establishments (fig. 66). This worm does not injure grain or cereal products 

but is a predator on other insects found in mills and warehouses. A closely related species, 

Scenopinus glabrifrons Meigen,26 is also known as a windowpane fly.

 

23Hymenoptera, Bethylidae.

24Hymenoptera, Braconidae.

25Hymenoptera, Ichneumonidae.

26Diptera, Scenopinidae.
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Figure 63. Braecon hebetor S. adult female, in three poses: A, feeding on body fluids of

Mediterranean flour moth larva, with straight ovipositor protruding behind: B, in position for puncturing body 

of larva preparatory to laying an egg: C, with ovipositor well inserted in larva, just before laying an egg.

A

B

C
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Page 61

Figure 64. Venturia canescens adult Enlarged.

Figure 65. Larva of windowpane fly. Scenopinus lenestralis (L.), about three-fourths of an inch long. La►a 

preys upon grain beetles and mites.

Figure 66. Windowpane fly. Suenopinus fenesiralis (L.), adult.
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HOW GRAIN BECOMES INFESTED

Grain may become infested in a number of ways. In many grain-growing regions. infestation 

starts in the field before the crops are harvested. This is. of course, particularly true in the South. 

where the rice weevil and other insects are abundant in the field at harvesttime, and in the soft 

red winter wheat region of the Eastern States, where the Angoumois grain moth is often extremely 

destructive. In the more northern States that experience severe winters. field infestation is 

negligible.

In addition to field infestation. which may he important (depending on the region or the season). 

there are several other sources of infestation of stored grain that are of considerable importance.

In all regions, it is customary to store grain year after year in the same bins. If these bins are made 

of wood, cracks and crevices become filled with grain dust and broken grain and afford places of 

concealment for many insects. Insects such as the cadelle burrow into the wooden sides or floors 

to pupate and later emerge in enormous numbers. Grain bins are not always properly cleaned; 

hence, fresh grain stored in them quickly becomes infested.

Storing bran, shorts, and other milled feeds in or near the granary is another cause of infestation, 

since these products are invariably infested. Many bins, too, are located in barns that normally 

contain products in which insects breed.

Temporary storage of grain in country or crib elevators frequently adds to the danger of infestation. 

Such storage is difficult to keep free from infestation, and clean grain often becomes contaminated 

by infested grain brought to the same place.

Grain may also become infested while moving it in railroad boxcars to terminal elevators. Many 

grain-infesting insects live in the grain dust and waste grain that accumulate in cracks of the floors 

or woodwork and in the linings of the boxcars.

Storage of clean grain in ware-houses and elevators that already contain infested grain also 

results in contamination through the movement of insects from the infested grain to the clean 

grain.

Before shipment, uninfested grain should not be placed in sacks previously used for grain storage 

because these old sacks often harbor insects, as shown in figure 21, unless they have been 

sterilized by heat or fumigation. Certain extensive and costly infestations have been traced directly 

to the use of secondhand, infested, untreated grain sacks.

Grain stored in open or poorly constructed cribs or bins may become infested by insects flying in 

from the outside.
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HOW TO PREVENT OR REDUCE PRIMARY INFESTATION

Adoption of the combine harvester has reduced field infestation of small grain to a negligible 

amount. To prevent infestation after harvest, it is recommended that producers take the following 

steps: 

(1) Store only dry grain in weather-tight, rodent-proof bins, preferably 

made of steel; 

(2) clean out all bins before loading with grain; 

(3) spray the walls and floors of wooden bins and around the door frames

 of metal bins; 

(4) clean up and dispose of litter, waste grain, and feed accumulations in 

and around farm buildings; 

(5) apply protective powder, or spray, directly to grain as it is binned, or 

fumigate promptly after binning; and 

(6) inspect the bins monthly and fumigate if an infestation is discovered.

In the North Central States, exposure to winter weather in most years kills off infestations in ear 

corn stored on the farm; hence, the loss from insect attack is not significant if the corn is to be 

used for feed during the ensuing season. Following mild winters, the Angoumois grain moth may 

he destructive, so under such conditions. it is well to shell corn in May and store it in tight bins. 

In the Southern States, field infestation can he reduced by: 

(1) Growing corn varieties with tight shucks that are semi-resistant to field

 infestation; 

(2) disposing of infested grain in farm storages before the corn reaches 

the silking stage; 

(3) early harvesting; 

(4) applying a protectant; 

(5) drying and shelling; and 

(6) storing the corn in tight bins suitable for fumigation.

Information regarding the prevention or reduction of grain infestation is contained in other 

publications of the Department of Agriculture.
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The U.S. Department of Agriculture (USDA) prohibits discrimination in its programs on the basis of 

race, color, national origin, sex, religion, age, disability, political beliefs, and marital or familial status. 

(Not all prohibited bases apply to all programs.) Persons with disabilities who require alternate means 

for communication of program information (Braille, large print, audiotape, etc.) should contact USDA’s 

TARGET Center at (202) 720-2600 (voice and TDD).

To file a complaint, write to the USDA, Office of Civil Rights, Room 326-W, 1400 Independence Avenue, 

SW, Washington, DC 20250-9410, or call (202) 720-5964 (voice and TDD). USDA is an equal employment 

opportunity employer.