Forest Health Technology 

Enterprise Team—Morgantown

Guide to the Siricid Woodwasps

of North America

FHTET-2006-15

September 2006

Forest Health Technology

Enterprise Team

Technology 

Transfer

Siricid Guide

Forest

Service

U.S. Department 

of Agriculture

53$!

Nathan M. Schiff, Steven A. Valley,James R. LaBonte, and David R. Smith
The Forest Health Technology Enterprise Team (FHTET) was created in 1995 

by the Deputy Chief for State and Private Forestry, USDA, Forest Service, to 

develop and deliver technologies to protect and improve the health of American 

forests. This book was published by FHTET as part of the technology transfer 

series.

www.fs.fed.us/foresthealth/technology/

Cover photo: Lateral view of Sirex noctilio female.
Nathan M. Schiff,

1

 Steven A. Valley,

2

James R. LaBonte,

2 and David R. Smith3

1 USDA Forest Service, Southern Research Station,

Center for Bottomland Hardwoods Research

2 Oregon Department of Agriculture, Plant Division

3 USDA Agricultural Research Service, Plant Sciences Institute, 

Systematic Entomology Laboratory

Published by:

USDA Forest Service

Forest Health Technology Enterprise Team

Morgantown, West Virginia 26505 

September 2006

Guide to the Siricid Woodwasps

of North America
We thank all those who helped with this publication. Several individuals who deserve special mention 

include Ken Cote, Rick Hoebeke, Joe MacGown, Terry Schiefer, Sheryl Costello, Dennis Haugen,

Dan Wilson, Don Duerr, Kevin Dodds, Herman Hall, Pete Tolesano, Paul Lago, Mark Vardanega,

Mike Kroetch, Wood Johnson, Jim Meeker, Carl Olsen, Steve Heydon, Mike Niemela, Rick Westcott,

Alan Mudge, Larry Bezark, Johnathan Quine, Angela Horne, Ted Leininger, Sally McElway, Dan Miller,

Virginia Scott, Joshua Vlach, Amy Abel, Iral Ragenovich, Thomas J. Henry, and Noel Schneeberger.

Finally, we extend thanks to Juliette Watts, Helen Thompson, and Roberta Burzynski of the USDA Forest 

Service, Northeastern Area State and Private Forestry for layout and editing.

The hardware and software used to acquire the majority of images in this publication were obtained 

through funds provided by the USDA Animal and Plant Health Inspection Service–Plant Protection and 

Quarantine, the USDA Forest Service, and the State of Oregon Lottery.

For additional information, contact:

Nathan Schiff

USDA Forest Service

Southern Research Station

Center for Bottomland Hardwoods Research

PO Box 227

Stoneville, MS 38776

Phone: 662-686-3175

Fax: 662-686-3195

E-mail: nschiff@fs.fed.us

The use of trade or firm names in this publication is for reader information only and does not imply 

endorsement by the U.S. Department of Agriculture of any product or service.

Acknowledgments

For a copy of this guide, contact Noel Schneeberger in Newtown Square, Pennsylvania (Phone: 

610-557-4121, email: nschneeberger@fs.fed.us) or Patty Dougherty (Phone: 610-557-4225, email: 

pdougherty@fs.fed.us).
Table of Contents

Introduction ....................................................................................................................................................1

Woodwasp Biology..........................................................................................................................................2

Identifying Siricidae ........................................................................................................................................3

 General Description ................................................................................................................................3

 Size and Color Variation .........................................................................................................................3

How to Use This Guide...................................................................................................................................4

Keys.................................................................................................................................................................5

 Key to Genera of Siricidae of North America.........................................................................................6

 Subfamily Tremicinae......................................................................................................................9

 Eriotremex formosanus (Matsumura)................................................................................9

 Tremex columba (Linnaeus)............................................................................................13

 Subfamily Siricinae........................................................................................................................16

 Key to Sirex Species...............................................................................................................16

 Sirex areolatus (Cresson) ................................................................................................19

 Sirex behrensii (Cresson) ................................................................................................23

 Sirex cyaneus Fabricius ...................................................................................................27

 Sirex edwardsii Brullé.....................................................................................................31

 Sirex juvencus californicus (Ashmead).............................................................................35

 Sirex juvencus juvencus (Linnaeus)..................................................................................39

 Sirex longicauda Middlekauff.........................................................................................43

 Sirex nigricornis Fabricius ..............................................................................................45

 Sirex noctilio Fabricius....................................................................................................49

 Sirex varipes Walker.......................................................................................................53
 Key to Urocerus Species..........................................................................................................56

 Urocerus albicornis (Fabricius).........................................................................................59

 Urocerus californicus Norton ...........................................................................................63

 Urocerus cressoni Norton.................................................................................................67

 Urocerus gigas flavicornis (Fabricius)...............................................................................71

 Urocerus sah (Mocsáry)...................................................................................................75

 Urocerus taxodii (Ashmead)............................................................................................77

 Key to Xeris Species...............................................................................................................80

 Xeris morrisoni indecisus (MacGillivray).........................................................................83

 Xeris morrisoni morrisoni (Cresson)................................................................................87

 Xeris spectrum spectrum (Linnaeus).................................................................................91

 Xeris spectrum townesi Maa ............................................................................................95

 Xeris tarsalis (Cresson)...................................................................................................97

About the Images........................................................................................................................................100

Selected References .....................................................................................................................................101


The Siricidae are a family of large, colorful, 

stingless wasps whose larvae bore into wood. They 

are members of the suborder Symphyta (sawflies, 

and horntails or woodwasps) of the insect order 

Hymenoptera (ants, wasps, and bees), and are 

characterized by having a broad waist and an 

ovipositor modified to insert eggs into wood.

Worldwide, the family Siricidae has approximately 

100 species in 2 subfamilies and 11 genera. The 

species are widely distributed in the forests of the 

Northern Hemisphere with some as far south as 

Cuba, northern Central America, New Guinea, 

the Philippines, Vietnam, northern India, and 

northern Africa. No species are known to be native 

to Australia or South America, but two species are 

known from tropical Africa.

In North America north of Mexico, there are 23 

species and subspecies of Siricidae in 5 genera 

representing both subfamilies: the Tremicinae, which 

are associated mostly with hardwoods, and the 

Siricinae, which feed on conifers. Several siricids in 

North America, such as Eriotremex formosanus and

Urocerus sah, were introduced from other countries 

with imported goods. Wood-boring larvae of siricids 

often take more than a year to develop. If they are 

not noticed when the wood is cut, they can be 

readily transported within lumber, furniture, or wood 

packing material to a new State or country. When 

their development is completed far from their 

country of origin, they emerge from the wood and 

start looking for hosts in their new habitat.

Introduction

While most species of siricids are of only minor 

importance in their native forests, exotic species can 

be quite damaging. Sirex noctilio, a species native 

to Europe, Asia, and North Africa, has been very 

destructive to plantations of introduced North 

American pines in several Southern Hemisphere 

countries. It was so destructive to Monterey pines 

in Australia and New Zealand that the Australians 

started a research program in the 1960s to control 

it. A European nematode, Deladenus siricidicola, has 

proven extremely effective as a classical biological 

control agent for Sirex noctilio in both Australia 

and New Zealand. In the last 25 years, Sirex noctilio

has been introduced accidentally to plantations of 

North American pines in South Africa and several 

South American countries. Currently, South Africa, 

Argentina, Uruguay, Chile, and Brazil have started 

control programs with this nematode.

In 2005, Sirex noctilio was discovered in New York 

and Canada. A program is being developed to 

control it, but there are unique problems in North 

America, the most basic of which is identification of 

this pest. In contrast to the Southern Hemisphere 

countries, which have no native siricid species, North 

America has many siricids, including several that are 

very similar to Sirex noctilio. This guide, including 

keys and photographic figures, was produced as a 

reference to help foresters, land managers, students, 

and all those concerned with our native forests 

identify North American Siricidae, including the 

introduced Sirex noctilio.
Woodwasp Biology

The biology of siricid woodwasps is a complex 

interaction between three organisms: the woodwasp, 

a symbiotic wood-decaying fungus, and the host 

tree. Woodwasp larvae, like most wood-boring 

insects, do not make enzymes that digest wood, so 

they require a symbiont to break down the wood. 

Siricids use wood-decaying fungi that females carry 

in specialized abdominal glands called mycangia. 

When a female lays eggs in a tree, she also inserts 

some of the fungus, which grows rapidly and 

excretes wood digesting enzymes. The larvae then 

feed on the fungus and digested wood. In some 

species, especially Sirex noctilio, the female also 

injects toxic mucus into the tree, which helps the 

fungus colonize the wood and kill the tree.

Depending on the species and the latitude, the 

woodwasp larva takes from 1 to 3 years to develop 

before the adult emerges, typically in the late 

summer or fall. Males emerge from the tree first 

and disperse, preventing inbreeding. They gather 

with other males high up in trees and wait for 

females. When females emerge, they fly to stressed 

or wounded trees to mate and lay their eggs. Many 

species of siricids in Western North America are 

attracted to forest fires presumably because fires 

stress or kill trees.

Siricids, like all Hymenoptera and some other 

insects, have a complex sex determination system 

called haplo-diploidy. In this arrangement, all the 

males are haploid with only one set of chromosomes, while females are diploid with two sets of 

chromosomes. Unmated females only produce male 

progeny while mated females can produce both male 

and female offspring. This system often results in 

skewed sex ratios when siricids are reared from a tree 

or piece of wood.

Siricids have several native predators and parasitoids 

in North America. The most common are large 

ichneumonid wasps in the genus Megarhyssa. 

These wasps have very long, thin ovipositors to 

lay their eggs on siricid larvae deep in the wood. 

Individuals of Megarhyssa can sometimes be 

followed to find siricid-infested trees. Occasionally, 

Megarhyssa females can be seen hanging from a 

tree by their ovipositors, which can become stuck 

during oviposition. A second family of wasps that 

parasitize Siricidae is the Ibaliidae. In general, 

Ibalia individuals, which have a distinctive, laterally 

compressed, oblong abdomen, are much smaller 

than Megarhyssa individuals and probably parasitize 

younger siricid larvae.

Perhaps the most significant organisms that attack 

siricids are parasitic nematodes in the family 

Neotylenchidae. There are several native species in 

North America; the European species, Deladenus 

siricidicola, has been used to control Sirex noctilio

in the Southern Hemisphere. These nematodes 

are quite remarkable, having two very different 

adult forms with different life cycles depending on 

their environment. In the presence of fresh fungus, 

juveniles develop into a fungus-feeding form. If the 

fungus is old or the juveniles are near a siricid larva, 

the nematodes develop into a parasitic form. The 

female parasitic nematodes penetrate the cuticle of 

the siricid larva and enter the body cavity. When 

the siricid pupates, the female nematode produces 

juvenile nematodes that feed on the eggs of female 

or the testes of male siricid hosts. Even though the 

nematodes have consumed her eggs, the female 

siricid continues to oviposit them into host trees, 

effectively spreading the nematodes. In this manner, 

these nematodes can spread through the forest and 

control the siricids.
General Description

Adult siricids have a typical insect body plan 

composed of three parts: head, thorax, and abdomen. 

Each part has its own set of distinguishing features 

or appendages. The head has the eyes, mouthparts, 

and antennae; the thorax has three pairs of legs and 

two pairs of membranous wings; and the abdomen 

has the digestive and reproductive organs. In the 

Siricidae, the abdominal appendages are quite 

distinctive. Both sexes have a short dorsal spine 

or horn at the apex of the abdomen called the 

cornus, giving rise to one of the common names 

for the family, horntail. Females also have a ventral 

ovipositor in a sheath. Since many of the body parts 

used in the keys have technical names that might be 

unfamiliar to the reader, they have been identified in 

the photograph on page 5.

Size and Color Variation

An unusual feature of siricids is that they exhibit 

extreme variation in body size. Fully developed 

adults of the same species may range in body length 

from 1 to 5 centimeters, excluding the ovipositor. 

This variation has been observed in many species 

and even among individuals reared from the same 

tree. Size cannot be used to distinguish species; the 

characters in the keys will be sufficient to identify 

small and large individuals.

Color is a useful character for identifying siricid 

species, but there can be considerable variation. 

We have tried to use contrasting characters such 

as red versus blue, and the keys should identify 

most specimens, but there are at least two kinds of 

variation that may be confusing. First, there is true 

variation where a color may not be as described or 

figured. Examples of this kind of color variation 

include some specimens of Urocerus cressoni, which 

Identifying Siricidae

do not appear to have white spots behind the eyes, 

and specimens of Tremex columba, which can vary 

from reddish brown to dark brown with yellow 

stripes. The second kind of color variation is seen in 

newly emerged specimens that were not completely 

tanned or hardened when killed. In these cases, the 

abdomen or appendages are a lighter color than 

expected.

We use the colors red and blue to describe body 

parts of many species in the keys and descriptions. 

Unfortunately, there are many shades of red and 

blue, and it is often difficult to agree on the exact 

shade of a particular body part. In this guide, 

therefore, red covers the range of shades from 

reddish brown through orange red to orange yellow, 

and blue covers the range from navy to black. In 

general, red is used as a contrast to blue or black.
This guide contains keys to genera and species, 

and photographs and descriptions of species and 

subspecies. It is designed so the user can identify 

most woodwasps by comparison of specimens 

with the species photographs. For each species, 

there are lateral and dorsal images to facilitate 

comparison. Females of most siricids are readily 

recognizable, except for a group of species in the 

genus Sirex that are blue with short ovipositors. 

These specimens need to be identified using the key 

to Sirex species on page 16. Males of most Sirex

species are uncommon and some of the species are 

not easily identifiable. The key takes Sirex species as 

far as possible with the characters available. We have 

tried to make the keys simple to use, with highly 

contrasting characters. Wherever characters are not 

obvious from the general images, we have provided 

detailed images in the keys. Note that not all images 

are to scale.

Until the user becomes familiar with the species, 

the best strategy is to determine the genus with 

the key to genera and then use the appropriate key 

to species. After a specimen is identified, it should 

be verified by comparison with the photographs 

and descriptions. The descriptive notes describe 

only females, as they are much more commonly 

encountered than males and descriptions of males 

would have to be detailed and lengthy. When the 

user becomes familiar with many of the species, 

the key characters can be used to abbreviate the 

identification process. The key characters are 

normally enough to separate the specimen from the 

species that is most similar to it.

If a species cannot be identified with certainty or 

if users believe they have discovered a population 

of Sirex noctilio, they should contact one of the 

following: State department of agriculture; State 

department of forestry; local cooperative extension 

office; USDA Animal and Plant Health Inspection 

Service, Plant Protection and Quarantine; or USDA 

Forest Service.

How to Use This Guide
Keys

The taxonomy of North American Siricidae is 

currently in a state of flux. Some characters used in 

the past are more variable than previously thought, 

and there are not enough specimens, especially 

males, to unambiguously define the limits of some 

species. Several species will likely be redefined in the 

future. As there is an immediate need for this guide, 

we have followed the Catalog of Hymenoptera in 

America North of Mexico (Smith 1979) to determine 

our list of species. We hope this guide and interest 

in Sirex noctilio will stimulate the collection of siricid 

specimens and lead to a revision of the family.

Femur

Tibia

Apical spines

Tarsus

Cornus

Sheath

Mesopleuron

Ovipositor
Key to Genera of Siricidae of North America

1. Antennae with less than 16 segments (figure 1) Tremex columba (page 13)

Antennae with more than 20 segments (figure 1) 2

2. Abdomen with long golden hairs Eriotremex formosanus (page 9)

Abdomen without long golden hairs 3

3. Head with pale spot behind eyes (figure 2);

 female cornus long and slender (figure 3) 4

Head behind eyes uniformly dark (figure 2);

 female cornus short and triangular (figure 3) Sirex (key on page 16)

4. Hind tibia with one apical spur (figure 4) Xeris (key on page 80)

Hind tibia with two apical spurs (figure 4) Urocerus (key on page 56)

Figure 1. Antennae of (top to bottom) Eriotremex, Tremex, Xeris, Urocerus, and Sirex.
Figure 2. Color variation of the area behind the eyes of siricids: top left, Sirex juvencus californicus completely 

dark; top right, Urocerus sah completely pale; bottom left, Urocerus taxodii with small pale spots; bottom right

Xeris morrisoni morrisoni with large pale spots.

Figure 3. Triangular cornus of Sirex (left) versus slender cornus of Xeris (center) and Urocerus (right).
Figure 4. Two apical spurs of Urocerus (top) versus one apical spur of Xeris (bottom).
Eriotremex formosanus (Matsumura)

Status: Exotic from southeastern Asia

Distribution: Southeastern United States (Alabama, Florida, Georgia, Louisiana, Mississippi, 

North Carolina, South Carolina, Texas, and Virginia)

Hosts: Oak, hickory, sweetgum, and probably other hardwoods. Females have been observed 

ovipositing into and sitting on pines.

Descriptive notes: Female Eriotremex formosanus are large brown- and yellow-striped wasps with short, 

blunt, black antennae. They appear similar to the striped form of Tremex columba, 

except that they have long golden hairs on the dorsum of the abdomen.

Key characters: Antennae short, blunt, black; abdomen with long yellow hairs on dorsum

Eriotremex formosanus, male dorsal

Eriotremex formosanus, male lateral Images of male Eriotremex formosanus by Joe MacGown.

SUBFAMILY TREMICINAE
1

0

Eriotremex formosanus, female dorsal
11Eriotremex formosanus, female lateral
12
13

Tremex columba, male lateral

Tremex columba, male dorsal

Tremex columba (Linnaeus)

Common name: Pigeon tremex

Status: Native

Distribution: In the East: Nova Scotia, New Brunswick, and Quebec, south to Florida then west to 

the Rockies. In the West: Colorado, Utah, Arizona, Mexico, and a few records from 

southern California.

Hosts: Beech, elm, hickory, maple, oak, poplar, apple, pear, sycamore, and hackberry.

Tremex columba will probably attack other deciduous hardwoods, especially trees that 

are weakened or dying.

Descriptive notes: Female Tremex columba are large wasps with short, blunt, brown antennae. There is 

considerable color variation in the species, but females tend to be dark to light brown 

with yellow stripes on the abdomen; males tend to be brown to orange with less 

distinctive markings.

Key characters: Antennae short, blunt, brown; abdomen without golden hairs
1

4

Tremex columba, female dorsal
15Tremex columba, female lateral
16

Key to Sirex Species

1. Female 2

Male 11

2. Abdomen red 3

Abdomen blue black 4

3. Wings black; Eastern North America Sirex nigricornis (page 45)

Wings banded; Western North America Sirex behrensii (page 23)

4. Ovipositor length medium or long (figure 5) 5

Ovipositor short (figure 5) 6

5. Ovipositor long (figure 5); tibiae and tarsi red Sirex longicauda (page 43)

Ovipositor medium length (figure 5); legs black Sirex areolatus (page 19)

6. Ovipositor with large pits close together (figure 6);

 mesopleuron densely punctured (figure 7);

 legs always red Sirex noctilio (page 49)

Ovipositor with small pits distantly spaced (figure 6); 

 mesopleuron with smooth areas between

 punctures (figure 7); legs red or black 7

7. Antennae reddish brown at base; legs red Sirex juvencus juvencus (page 39)

Antennae black; legs red or black 8

8. Legs black 9

Legs at least partially red 10

9. Eastern North America1 Sirex edwardsii (page 31)

Western North America1 Sirex juvencus californicus (page 35)

10. Legs red with blue surfaces; Pacific Northwest Sirex varipes (page 53)

Legs red Sirex cyaneus (page 27)

11. Abdomen reddish, black at base and apex 12

Abdomen reddish with only one or two basal

 segments black 16

1Woodwasps can be transported out of their native range with commerce, but, until the group is revised, geographic 

 range is a useful character.

SUBFAMILY SIRICINAE
17

Figure 5. Abdomens and ovipositors of (top to bottom) Sirex cyaneus (short), Sirex areolatus (medium), and 

Sirex longicauda (long).

12. Hind femur black 13

Hind femur red 15

13. Abdominal segments 3–7 yellow 14

Abdominal segments 5–6 yellow Sirex edwardsii (page 31)

14. Fore and mid tibiae and tarsi red Sirex longicauda (page 43)

Fore and mid tibiae and tarsi black Sirex areolatus (page 19)

15. Abdominal segments 4–7 yellow; antennae

 brownish at base Sirex juvencus juvencus (page 39)

Abdominal segments 3–7 yellow; antennae black Sirex noctilio (page 49)

16. Hind femur black Sirex nigricornis (page 45)

Hind femur red 17

17. Hind tibia, hind tarsus, and base of antennae red Sirex behrensii (page 23),

 Sirex juvencus californicus (page 35)

Hind tibia, hind tarsus, and base of antennae black Sirex cyaneus (page 27),

 Sirex varipes (page 53)
18

Figure 7. Mesopleura of (top to bottom) Sirex 

cyaneus, Sirex juvencus juvencus, and Sirex noctilio. The 

punctures in Sirex noctilio are much closer together 

than in the other species, which have smooth, shiny 

areas between punctures.

Figure 6. Ovipositors of (left to right) Sirex cyaneus, 

Sirex noctilio, and Sirex juvencus juvencus, showing pit 

size and spacing. The Sirex noctilio ovipositor has large pits that are close together. The Sirex juvencus juvencus

and Sirex cyaneus ovipositors have pits that are small 

relative to the width of the ovipositor, and they are 

relatively far apart. The scissors in this figure indicate 

that the ovipositors have been cut in half so that more 

of their length can be shown. Individual ovipositors are 

shown with the tip on the left and the basal portion on 

the right.
19

Sirex areolatus, male lateral

Sirex areolatus, male dorsal

Sirex areolatus (Cresson)

Status: Native

Distribution: Honduras, New Mexico, and Colorado through the Western United States and north 

to British Columbia. Specimens from Virginia, Florida, and Europe may be 

adventive, emerging from imported lumber.

Hosts: Cypress, juniper, incense cedar, pine, Douglas-fir, redwood, and baldcypress

Descriptive notes: Female Sirex areolatus are large blue-black wasps with medium-length ovipositors and 

blue-black legs. The wings are very light clear brown. The female specimen shown 

here has the head pushed forward, exposing white neck muscles. This white area is not 

visible in most specimens.

Key characters: Body and legs blue; ovipositor medium length
20

Sirex areolatus, female dorsal
21Sirex areolatus, female lateral
22
23

Sirex behrensii (Cresson)

Status: Native

Distribution: Idaho, Nevada, Washington, Oregon, and California

Hosts: Cypress and pine

Descriptive notes: Female Sirex behrensii are large blue or black wasps with red abdomens and black 

antennae. The wings are hyaline with two distinct dark bands.

Key characters: Abdomen red; wings banded; Western North America

Sirex behrensii, male lateral

Sirex behrensii, male dorsal
24

Sirex behrensii, female dorsal
25Sirex behrensii, female lateral
26
27

Sirex cyaneus Fabricius

Common name: Blue horntail

Status: Native

Distribution: Newfoundland to British Columbia, south to North Carolina, Illinois, Kansas, and 

California; also New Mexico and Europe

Hosts: Fir, larch, spruce, pine, and Douglas-fir

Descriptive notes: Female Sirex cyaneus are large blue wasps with short ovipositors and reddish-yellow 

legs. The wings vary from hyaline to dark. Sirex cyaneus looks very similar to Sirex 

noctilio. It can be separated from Sirex noctilio by the very small, distantly spaced 

pits on the ovipositor and flattened spaces between punctures on the mesopleuron. 

Sirex cyaneus can be separated from Sirex juvencus juvencus by the color of the 

antennae.

Key characters: Ovipositor short; body blue; legs reddish yellow; ovipositor with widely spaced pits; 

flattened spaces between mesopleural punctures

Sirex cyaneus, male lateral

Sirex cyaneus, male dorsal
28

Sirex cyaneus, female dorsal
29Sirex cyaneus, female lateral
30
31

Sirex edwardsii Brullé

Status: Native

Distribution: Quebec to Georgia and Alabama, west to Saskatchewan, Wisconsin, Arkansas, 

Louisiana, Mississippi

Hosts: Spruce and pine

Descriptive notes: Female Sirex edwardsii are large blue-black wasps with short ovipositors, blueblack legs, and uniformly dark brown wings. This species is similar to dark-winged 

forms of Sirex juvencus californicus. Currently, the easiest way to separate them is by 

geographical range.

Key characters: Body blue black; wings black; Eastern North America

Sirex edwardsii, male lateral

Sirex edwardsii, male dorsal
32

Sirex edwardsii, female dorsal
33Sirex edwardsii, female lateral
34
35

Sirex juvencus californicus (Ashmead)

Status: Native

Distribution: Western North America (British Columbia, Alberta, Washington, Oregon, California,

Montana, Wyoming, Colorado, South Dakota, Utah, New Mexico, and Mexico)

Hosts: Cypress, larch, pine, and Douglas-fir

Descriptive notes: Female Sirex juvencus californicus are large blue wasps with short ovipositors and 

dark-blue legs. The wings range from hyaline with two smoky brown bands to

uniformly black.

Key characters: Ovipositor short; body and legs blue; Western North America

Sirex juvencus californicus, male lateral

Sirex juvencus californicus, male dorsal
36

Sirex juvencus californicus, female dorsal
37Sirex juvencus californicus, female lateral
38
39

Sirex juvencus juvencus (Linnaeus)

Status: Presumably introduced

Distribution: Canada (Labrador, Newfoundland, Nova Scotia, New Brunswick, British Columbia, 

and the Yukon Territory). In the United States, it is recorded from New Jersey. It is

native to Europe and Asia, and has been intercepted in New Zealand, Australia, and

the Philippines.

Hosts: Fir, larch, spruce, and pine

Descriptive notes: Female Sirex juvencus juvencus are large blue wasps with red legs, short ovipositors, 

and hyaline wings. The basal segments of the antennae of both sexes are often reddish 

brown (see photo below), as opposed to completely black in Sirex cyaneus.

Key characters: Ovipositor short; body blue; legs red; base of antennae reddish

Sirex juvencus juvencus,

male lateral

Sirex juvencus juvencus, male dorsal

Sirex juvencus juvencus, antennal segments
40

Sirex juvencus juvencus, female dorsal
41Sirex juvencus juvencus, female lateral
42
43

Sirex longicauda Middlekauff

Status: Native

Distribution: California, Colorado, Idaho, Montana, Nevada, New Mexico, Oregon, and Utah.

There are records from several Eastern States (Kansas, Nebraska, Ohio, Virginia, and

West Virginia), but these wasps probably emerged from wood infested in Western

States.

Hosts: Fir, pine, and Douglas-fir

Descriptive notes: Female Sirex longicauda are large blue wasps with red legs and extremely long 

ovipositors.

Key characters: Body blue; ovipositor very long

Sirex longicauda, male lateral

Sirex longicauda, male dorsal
44

Sirex longicauda, female dorsal Sirex longicauda, female lateral
45

Sirex nigricornis Fabricius

Status: Native

Distribution: Quebec to Florida, west to Saskatchewan, Wisconsin, Ohio, Indiana, Arkansas, 

Louisiana, Mississippi, and Texas

Hosts: Pine and spruce

Descriptive notes: Female Sirex nigricornis are large black wasps with uniformly dark wings and red 

abdomens. The eye color of the male specimens shown is an artifact of preservation; 

most male specimens have dark eyes.

Key characters: Abdomen red; wings uniformly dark; Eastern North America

Sirex nigricornis, male lateral

Sirex nigricornis, male dorsal
46

Sirex nigricornis, female dorsal
47Sirex nigricornis, female lateral
48
49

Sirex noctilio Fabricius

Common names: Sirex woodwasp and European woodwasp

Status: Exotic from Europe, Asia, and North Africa. Introduced to Australia, New Zealand, 

South Africa, South America, and North America.

Distribution: Ontario, Manitoba, New York, and Pennsylvania

Hosts: Fir, larch, spruce, pine, and Douglas-fir

Descriptive notes: Female Sirex noctilio are blue wasps with short ovipositors and red legs. They can be 

separated from Sirex cyaneus by the large, closely spaced pits on the ovipositor and 

the absence of smooth shiny areas between punctures on the mesopleuron.

Key characters: Body blue; legs red; ovipositor short with large, closely spaced pits; mesopleuron 

densely punctured

Sirex noctilio, male lateral

Sirex noctilio, male dorsal
50

Sirex noctilio, female dorsal
51Sirex noctilio, female lateral
52
53

Sirex varipes Walker

Status: Native

Distribution: British Columbia, Washington, Oregon, California, Nevada, and Montana

Hosts: Fir, spruce, and pine

Descriptive notes: Female Sirex varipes are large blue wasps with short ovipositors and red legs that 

have blue on the outer surfaces. Males of this species are not well characterized; 

they are recognized by association with females caught at the same time.

Key characters: Body blue; legs red with blue sheen on forward surfaces

Sirex varipes, male dorsal Sirex varipes, male lateral
54

Sirex varipes, female dorsal
55Sirex varipes, female lateral
56

Key to Urocerus Species

1. Female 2

Male 7

2. Wings brown to black 3

Wings pale to bright yellow 5

3. Abdomen black 4

Abdomen mostly red Urocerus cressoni (page 67)

4. Cornus yellowish brown to orange Urocerus taxodii (page 77)

Cornus black Urocerus albicornis (page 59)

5. Thorax with yellow markings Urocerus sah (page 75)

Thorax black 6

6. Abdomen black Urocerus californicus (page 63)

Abdomen yellow at base and with a yellow band Urocerus gigas flavicornis (page 71)

7. Head mostly yellow to yellow orange Urocerus sah (page 75)

Head largely black with two pale spots behind eyes 8

8. Abdomen red; wings dark 9

Abdomen black and yellow or reddish; wings yellow 10

9. Legs black Urocerus cressoni (page 67)

Legs with dark orange on fore and mid legs,

 and white on hind legs Urocerus taxodii (page 77)

10. Abdomen reddish; wings yellow Urocerus californicus (page 63)

Abdomen black with broad yellow band 11

11. Hind basitarsus 4.0–5.5 times longer than broad

 (figure 8) Urocerus gigas flavicornis1

 (page 71)

Hind basitarsus 6.5–8.0 times longer than broad

 (figure 8) Urocerus albicornis (page 59)

1 There are several subspecies of Urocerus gigas in Europe and Asia. Urocerus gigas flavicornis is native to North 

 America.
57

Figure 8. Lateral view of hind basitarsus of male Urocerus gigas flavicornis (4.0–5.5 times longer than broad) 

(top) compared with male Urocerus albicornis (6.5–8.0 times longer than broad) (bottom).
58
59

Urocerus albicornis, male lateral

Urocerus albicornis,

male dorsal

Urocerus albicornis (Fabricius)

Status: Native

Distribution: Newfoundland to British Columbia, south to North Carolina, Michigan, Missouri,

New Mexico, California, Oregon, and Washington

Hosts: Fir, larch, spruce, pine, Douglas-fir, hemlock, and western redcedar

Descriptive notes: Female Urocerus albicornis are large black wasps with uniformly brown wings. There 

are two white spots on the head, the antennae are white except at the base and tips, 

and the femora and tibiae are white at the base and black distally.

Key characters: Body black; antennae white; wings brown
60

Urocerus albicornis, female dorsal
61Urocerus albicornis, female lateral
62
63

Urocerus californicus Norton

Status: Native

Distribution: Montana, Colorado, and New Mexico, west to British Columbia, Washington,

Oregon, and California

Hosts: Fir, larch, incense cedar, spruce, Douglas-fir, and hemlock

Descriptive notes: Female Urocerus californicus are large black wasps with bright yellow wings, yellow 

antennae, and two yellow spots behind the eyes. The femora and tibiae are yellow at 

the base and black distally.

Key characters: Body black; antennae yellow; wings bright yellow

Urocerus californicus, male dorsal

Urocerus californicus, male lateral
64

Urocerus californicus, female dorsal
65Urocerus californicus, female lateral
66
67

Urocerus cressoni Norton

Status: Native

Distribution: Nova Scotia, New Brunswick, Quebec, and Ontario south to Florida and west to 

Wisconsin, Minnesota, and Montana

Hosts: Fir, spruce, and pine

Descriptive notes: Female Urocerus cressoni are large wasps with black heads and thoraxes, red abdomens, 

and brown wings. There are two white spots behind the eyes and the antennae are 

black with white tips. The male is very similar to the female in coloration.

Key characters: Head and thorax black; abdomen red; antennae white-tipped

Urocerus cressoni, male dorsal Urocerus cressoni, male lateral
68

Urocerus cressoni, female dorsal
69Urocerus cressoni, female lateral
70
71

Urocerus gigas flavicornis (Fabricius)

Status: Native

Distribution: Labrador to Alaska, south to New Hampshire, Colorado, New Mexico, Arizona, and 

California

Hosts: Fir, larch, spruce, pine, and Douglas-fir

Descriptive notes: Female Urocerus gigas flavicornis are large black wasps with two yellow bands at 

the base and the middle of the abdomen, and two yellow spots behind the eyes.

The antennae are yellow and the wings are hyaline with a faint yellow tinge. The 

femora are black with yellow tibiae and tarsi.

Key characters: Body black; abdomen with yellow bands; antennae yellow

Urocerus gigas flavicornis, male lateral

Urocerus gigas flavicornis, male dorsal
72

Urocerus gigas flavicornis, female dorsal
73Urocerus gigas flavicornis, female lateral
74
75

Urocerus sah (Mocsáry)

Status: Exotic

Distribution: North Africa, Asia Minor, the Near East, and southern Russia. It is adventive in New 

Hampshire.

Hosts: Fir, spruce, and pine

Descriptive notes: Female Urocerus sah are black with yellow wings, antennae, upper half of 

mesepisternum, and legs except hind femora and basal two-thirds of hind tibiae. 

There is a yellow band across the abdomen and the yellow on the top of the head is 

continuous, not with two discrete spots like North American species of Urocerus.

Male Urocerus sah have not been collected in North America; therefore, no 

specimens could be photographed for this guide.

Key characters: Head with entire area behind the eyes yellow, not just discrete spots

Urocerus sah, female lateral
76

Urocerus sah, female dorsal
77

Urocerus taxodii (Ashmead)

Status: Native

Distribution: Florida, Mississippi, Missouri, Virginia, and Washington, DC

Hosts: Baldcypress

Descriptive notes: Female Urocerus taxodii are black medium-sized wasps with dark wings, white-tipped 

antennae, white spots behind the eyes, and a long, light-brown cornus. Males are 

similar to females except the abdomen is orange and the wings are hyaline.

Key characters: Apical antennal segments pale; cornus light brown to yellow

Urocerus taxodii, male lateral

Urocerus taxodii, male 

dorsal
78

Urocerus taxodii, female dorsal
79Urocerus taxodii, female lateral
80

Key to Xeris Species

1. Female 2

Male 4

2. Abdomen red 3

Abdomen black Xeris spectrum1

 (pages 91 and 95)

3. Cornus constricted in the middle (figure 9) Xeris morrisoni1 (pages 83 and 87)

Cornus not constricted in the middle (figure 9) Xeris tarsalis (page 97)

4. Abdomen black Xeris spectrum1

 (pages 91 and 95)

Abdomen mostly red 5

5. Top of head coarsely and densely pitted around median

 line; no polished areas along median line (figure 10) Xeris tarsalis (page 97)

Top of head sparsely pitted; polished areas

 flanking median line (figure 10) Xeris morrisoni1

 (pages 83 and 87)

Figure 9. Cornus of (left to right) Xeris tarsalis, Xeris morrisoni indecisus, and Xeris spectrum townesi.

1

 Xeris spectrum and Xeris morrisoni each have two subspecies:

· Xeris spectrum spectrum has broad white longitudinal stripes on the upper corners of the pronotum and black 

 antennae.

· Xeris spectrum townesi has a black pronotum, and the antennae vary from entirely reddish to black at the base 

 with a red tip.

· Xeris morrisoni morrisoni has legs and antennae that are black basally and red distally.

· Xeris morrisoni indecisus has legs and antennae that are uniformly red, except the two basal segments of the 

 antennae may be black.
81

Figure 10. Top of head of Xeris tarsalis (top) and Xeris morrisoni morrisoni (bottom) 

showing pitting around median line.
82
83

Xeris morrisoni indecisus (MacGillivray)

Status: Native

Distribution: British Columbia, Washington, Oregon, California, Nevada, Idaho, and Utah

Hosts: Fir, incense cedar, spruce, hemlock, Douglas-fir, and larch

Descriptive notes: Female Xeris morrisoni indecisus are large, slender wasps with very long ovipositors 

and red abdomens, legs, and antennae. They have two white spots behind the eyes and 

the wings are hyaline with faint smoky bands. The cornus is constricted in the middle.

Key characters: Cornus constricted; legs uniformly red

Xeris morrisoni indecisus, male dorsal Xeris morrisoni indecisus, male lateral
84

Xeris morrisoni indecisus, female dorsal
85Xeris morrisoni indecisus, female lateral
86
87

Xeris morrisoni morrisoni (Cresson)

Status: Native

Distribution: Arizona and Colorado

Hosts: Fir, spruce, and Douglas-fir

Descriptive notes: Female Xeris morrisoni morrisoni are large, slender wasps with very long ovipositors 

and red abdomens. Their legs and antennae are black at the base and red distally. They 

have two white spots behind the eyes and the wings are hyaline with faint smoky 

bands. The cornus is constricted in the middle.

Key characters: Cornus constricted; legs dark at base and red distally

Xeris morrisoni morrisoni, Xeris morrisoni morrisoni, male lateral

male dorsal
88

Xeris morrisoni morrisoni, female dorsal
89Xeris morrisoni morrisoni, female lateral
90
91

Xeris spectrum spectrum (Linnaeus)

Status: Native to North America, Europe, Asia, and North Africa

Distribution: New Brunswick, Connecticut, Michigan, Colorado, Arizona, Washington, Oregon,

and California

Hosts: Fir, larch, spruce, pine, and Douglas-fir

Descriptive notes: Female Xeris spectrum spectrum are large, slender black wasps with very long 

ovipositors, black antennae, and red legs. They have two white spots behind the eyes, 

lateral white margins along the pronotum, and the wings are hyaline with faint smoky 

bands. At this time, subspecies of male Xeris spectrum cannot be differentiated. We 

have included a photograph of the species for general reference.

Key characters: Antennae black; pronotum with white lateral margins

Xeris spectrum, male lateral
92

Xeris spectrum spectrum, female dorsal
93Xeris spectrum spectrum, female lateral
94
95

Xeris spectrum townesi Maa

Status: Native

Distribution: British Columbia, Washington, Oregon, California, Nevada, and Montana

Hosts: Fir, spruce, Douglas-fir, pine, and hemlock

Descriptive notes: Female Xeris spectrum townesi are large, slender black wasps with very long

ovipositors and red legs. The antennae vary from black at the base with red at the 

apex to all red. There are two white spots behind the eyes, and the wings are hyaline 

with faint smoky bands. At this time, subspecies of male Xeris spectrum cannot be 

differentiated. We have included a photograph of the species for general reference

under the description of Xeris spectrum spectrum on page 91.

Key characters: Distal portion of antennae or entire antennae pale reddish; entire pronotum black

Xeris spectrum townesi, female lateral
96

Xeris spectrum townesi, female dorsal
97

Xeris tarsalis (Cresson)

Status: Native

Distribution: Washington, Oregon, California, and Mexico

Hosts: Cypress, juniper, incense cedar, and possibly northern white cedar

Descriptive notes: Female Xeris tarsalis are large, slender wasps with long ovipositors, hyaline wings, 

and black antennae with red tips. They have two white spots behind the eyes and legs 

that are dark at the base and light at the apex. Males are similar to females in color

except the tip of the abdomen is black. The cornus is uniformly wide at the middle,

not constricted.

Key characters: Head and thorax black; abdomen red; cornus not constricted

Xeris tarsalis, male lateral

Xeris tarsalis, male dorsal
98

Xeris tarsalis, female dorsal
99Xeris tarsalis, female lateral
100

Our goal was to produce images to make 

identifications easy for both specialists and 

nonspecialists. The images were taken at the Oregon 

Department of Agriculture with a Leica MZ16 

stereoscope with axial imaging fitted with a Spot 

InsightTM digital camera. Depth of focus is extremely 

shallow when subjects are photographed through a 

microscope because, as magnification increases, the 

focus zone becomes a plane of decreasing depth. 

This is a significant problem in photomacrography, 

especially when the subject is a three-dimensional 

object like an insect. One way to increase the depth 

of focus is to decrease the size of the aperture, but 

this decreases the amount of light reaching the 

camera and introduces an effect called diffraction, 

which degrades image sharpness.

Our solution with the Leica system is to take a 

series of images, each of which has a shallow plane 

in focus but together make a “stack” of images from 

the top to the bottom of the subject. We process the 

stack digitally to combine the sharp (in focus) pixels 

from each layer. The resulting composite image has 

sharp focus throughout its depth. This process has 

challenges of its own. Further digital processing is 

necessary to remove artifacts of combining the stack, 

to sharpen the image, and—where possible—to 

remove distracting objects from the image, such 

as dirt, dust, and insect pins. Lighting is a critical 

component of this technique because we want to 

show not only color, but shape, surface texture, 

and topography, as well as shininess and metallic 

reflectance. The subjects of this project were usually 

too large to fit in the field of view of the scope, so 

images of small portions of each specimen were 

photographed in a grid pattern. The “tiles” of all the 

grids were then stitched together to create an image 

of the whole insect.

The specimens themselves created challenges 

because they were often covered with dirt, debris, 

and sometimes other artifacts introduced by traps 

or other collecting methods. Specimens of many 

species are rare, fragile, and difficult or impossible to 

clean without damage, and they were rarely pinned 

in the most photogenic poses.

The computer software controlling the microscope 

and camera, and creating the extended depthof-focus composite was Image-Pro®

 Plus 

(Media Cybernetics, Inc.) and In-Focus (Meyer 

Instruments, Inc.). Adobe® Photoshop® was used for 

all other post-capture processing, including stitching 

the tile segments of each image together.

All images, except for those of male Eriotremex 

formosanus, were taken by Steven Valley.

About the Images
101

The following references are provided for those readers who would like to further investigate the biology and 

identification of siricid woodwasps.

Bedding, R.A. 1972. Biology of Deladenus siricidicola (Neotylenchidae) an entomophagous nematode 

parasitic in siricid woodwasps. Nematologica. 18: 482–493.

Bedding, R.A.; Akhurst, R.J. 1974. Use of the nematode Deladenus siricidicola in the biological control of 

Sirex noctilio in Australia. Journal of the Australian Entomological Society. 13: 129–137.

Benson, R.B. 1943. Studies in Siricidae, especially of Europe and southern Asia (Hymenoptera: Symphyta). 

Bulletin of Entomological Research. 34: 27–51.

Buchner, P. 1965. Endosymbiosis of animals with plant microorganisms. New York: John Wiley & Sons, Inc. 

909 p.

Cameron, E.A. 1967. Notes on Sirex juvencus californicus (Hymenoptera: Siricidae), with a description of the 

male and a key to the California species of Sirex. Canadian Entomologist. 99: 18–24.

Cartwright, K. St. G. 1929. Notes on fungus associated with Sirex cyaneus. Annals of Applied Biology.

16: 182–187.

Haugen, D.A.; Underdown, M.G. 1990. Sirex noctilio control program in response to the 1987 Green 

Triangle outbreak. Australian Forestry. 53(1): 33–40.

Hoebeke, E.R.; Haugen, D.A.; Haack, R.A. 2005. Sirex noctilio: discovery of a Palearctic siricid woodwasp in 

New York. Newsletter of the Michigan Entomological Society. 50(1–2): 24–25.

Kukor, J.J.; Martin, M.M. 1983. Acquisition of digestive enzymes by siricid woodwasps from their fungal 

symbiont. Science. 220: 1161–1163.

Maa, T. 1949. A synopsis of Asiatic Siricoidea with notes on certain exotic and fossil forms (Hymenoptera: 

Symphyta). Notes d’Entomologie Chinoise. 13(2): 11–189.

Middlekauff, W.W. 1960. The siricid wood wasps of California (Hymenoptera: Symphyta). Bulletin of the 

California Insect Survey. 6: 59–77

Middlekauff, W.W. 1962. Notes and description of the previously unknown male of Sirex longicauda. PanPacific Entomologist. 38: 31–32.

Morgan, F.D. 1968. Bionomics of the Siricidae. Annual Review of Entomology. 13: 239–256.

Parkin, E.A. 1941. Symbiosis in larval Siricidae. Nature. 147: 329.

Selected References
102

Smith, D.R. 1978. Suborder Symphyta (Xyelidae, Pararchexyelidae, Parapamphiliidae, Xyelydidae, 

Karatavitidae, Gigasiricidae, Sepulcidae, Pseudosiricidae, Anaxyelidae, Siricidae, Xiphydriidae, 

Paroryssidae, Xyelotomidae, Blasticotomidae, Pergidae). In: van der Vecht, J.; Shenefelt, R.D., eds. 

Hymenopterorum catalogus, pars 14. The Hague: Dr. W. Junk B.V. Publishers. 193 p.

Smith, D.R. 1979. Symphyta. In: Krombein, K.V.; Hurd, P.D., Jr.; Smith, D.R.; Burks, B.D., eds. Catalog of 

Hymenoptera in America north of Mexico, Volume 1. Washington, DC: Smithsonian Institution Press: 

3–132.

Smith, D.R. 1987. Urocerus sah (Mocsáry) (Hymenoptera: Siricidae) new to North America and key to 

North America species of Urocerus. Proceedings of the Entomological Society of Washington. 89: 

834–835.

Smith, D.R. 1988. A synopsis of the sawflies (Hymenoptera: Symphyta) of America south of the United 

States: Introduction, Xyelidae, Pamphiliidae, Cimbicidae, Diprionidae, Xiphydriidae, Siricidae, Orussidae, 

Cephidae. Systematic Entomology. 13: 205–261.

Smith, D.R. 1996. Discovery and spread of the Asian horntail, Eriotremex formosanus (Matsumura) 

(Hymenoptera: Siricidae), in the United States. Journal of Entomological Science. 31(2): 116–171.

Smith, D.R.; Schiff, N.M. 2002. A review of the siricid woodwasps and their ibaliid parasitoids 

(Hymenoptera: Siricidae, Ibaliidae) in the Eastern United States, with emphasis on the Mid-Atlantic 

region. Proceedings of the Entomological Society of Washington. 104: 174–194.

Stange, L.A. 1996. The horntails of Florida (Hymenoptera: Siricidae). Division of Plant Industry 

Entomology Circular #376. Gainesville, FL: Florida Department of Agriculture and Consumer Services, 

Division of Plant Industry. 3 p.

Stillwell, M.A. 1966. Woodwasps (Siricidae) in conifers and the associated fungus, Stereum chailletii in 

Eastern Canada. Forest Science. 12: 121–128.

Stillwell, M.A. 1967. The pigeon tremex, Tremex columba (Hymenoptera: Siricidae), in New Brunswick. 

Canadian Entomologist. 99: 685–689.
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