Imported Fire Ants: An

Agricultural Pest and a

Human Health Hazard

Imported fire ants (Solenopsis invicta Buren, S. richteri Forel, and their hybrid) were accidentally introduced to the United States. The black imported fire

ant was brought to Mobile, AL, in 1918. The red

imported fire ant arrived in the 1930s. Since then,

they have become established across the South and

in parts of California and other Western States.

These pests pose serious threats to people, small

animals, and agricultural equipment. As these

insects spread northward and westward, more people

are asking the U.S. Department of Agriculture’s

(USDA) Animal and Plant Health Inspection Service

(APHIS) for advice about how to manage imported

fire ants. This factsheet answers several frequently

asked questions. 

Q: Why are they called fire ants?

A: Anyone who has been stung by one or more of

these aggressive insects can answer this question.

Fire ants clamp onto their targets with powerful jaws

and sting their victims repeatedly. Each sting injects

a dose of venom that causes a burning sensation.

The stings raise itching blisters that can become

infected. In sensitive victims, the stings can cause

anaphylactic shock (symptoms include trouble

breathing and fainting) or even death.

Q: What damage do fire ants cause?

A: Fire ants attack and sometimes kill newborn

domestic animals as well as pets and wildlife. Fire

ants can also destroy seedling corn, soybeans, and

other crops. These insects feed on buds or fruits of

many plants and may remove bands of bark from

young citrus trees, often killing them. Additionally,

the hard, cone-shaped nests of fire ants can mount

as high as 2 feet, making it difficult to cultivate and

harvest crops from infested fields. These fire ant

mounds are unsightly hazards in yards, parks, and

other recreational areas, where they are especially

dangerous to children and pets.

Q: Where are imported fire ants in the United

States, and where do they come from?

A: Imported fire ants were accidentally brought to

the United States from South America. Since arriving

in Mobile, AL, they have spread to 14 States and

Commonwealths. They now infest all or part of

Alabama, Arkansas, California, Florida, Georgia,

Louisiana, Mississippi, New Mexico, North Carolina,

Oklahoma, Puerto Rico, South Carolina, Tennessee,

and Texas.

Q: How can you identify fire ants?

A: Identifying fire ants is difficult because they look

much like ordinary ants. They are 1/8 to 1/4 inch

long and reddish brown to black in color. Fire ants

are probably best distinguished by their aggressive

behavior and characteristic mound-shaped nests.

Q: How does a colony begin?

A: A new colony begins with a “nuptial flight” of

winged males and winged females, usually on a

warm, spring day. After mating occurs, males drop to

the earth and die. Females that successfully elude

predators and survive drought and rain seek out

nesting sites and burrow underground. A new queen

sheds her wings and lays 12 to 24 worker eggs,

which she tends to constantly. Upon hatching, the

workers, all of which are sterile females, take over all

colony functions except reproduction, while the

queen only mates and lays eggs. She may produce

more than 200 eggs per day.

Q: How large is a colony?

A: Fire ant colonies vary in size, but a mature, 3-

year-old colony typically contains 250,000 workers,

which are sterile females, and hundreds of reproductive males and potentially reproductive females. A

colony population can grow to 300,000 ants. In addition to single-queen colonies, many fire ant colonies

have multiple queens, increasing tenfold the number

of mounds in a single acre.

Q: How do fire ants spread?

A: Limited local dispersal occurs during the mating

process, mass movement of colonies, and floods.

Ants travel longer distances by hitchhiking in motor

vehicles and in or on soil, plants with roots and soil

attached, nursery stock, sand, gravel, grass, sod,

hay, wood, or soil-moving equipment.

Factsheet 

Plant Protection and Quarantine A ril 2006

APHIS 
Q: What is USDA doing to prevent this spread?

A: APHIS works to limit the spread of imported fire

ants by requiring that all nursery stock and other

items likely to carry the pests be inspected and treated before traveling from fire ant-infested areas to fire

ant-free areas. Regulated articles include soil, plants

with roots and soil attached (except house plants

maintained indoors and not for sale), grass sod, baled

hay, and straw that have been stored in contact with

soil, and used soil-moving equipment.

Q: How can these pests be controlled?

A: Control of fire ants is made difficult by the protective behavior of the workers who guard the queen. If

the colony is disturbed, workers will hurriedly carry the

queen to a safe location. There, the queen begins a

new colony. Therefore, the best control is not a

method that will merely kill workers but a bait that will

be taken back to the nest by foraging ants where it

will either kill the queen or render her sterile. Baits

combine a food to attract the ants with an insecticide

or insect growth regulator (a pesticide that works by

disrupting the ants’ reproductive system). Although

baits are slow acting, they are often the best way to

reach the queen and eliminate the colony.

Q: How should treatments be applied?

A: Treatment options vary, depending on the type of

fire ant problem. Those applying any treatment

should read insecticide labels closely and follow all

directions. Some of the baits approved by the U.S.

Environmental Protection Agency include Amdro®,

Award®, Distance®, and Extinguish®. These should

be applied by broadcast method over the entire area

to be treated. Some contact insecticides may be also

be applied by broadcast over the entire area. Others

are to be applied to each mound. Many contact

insecticides are labeled for use on imported fire ant.

For more information on imported fire ants and

Federal restrictions imposed on the movement of 

regulated articles, contact one of the following:

• Your county’s agricultural extension agent, listed 

in the county government section of your tele

phone directory under Cooperative Extension 

Service.

• Your State’s regulatory officials, usually listed 

under department of agriculture, plant protection, 

or regulatory division in the State government 

section of your telephone directory.

• A Federal regulatory official, listed in the Federal 

Government section of your telephone directory 

under USDA, APHIS, Plant Protection and 

Quarantine. You can also contact APHIS through 

the World Wide Web by pointing your Web 

browser to http://www.aphis.usda.gov/ppq and 

using the “Comments” link to send a request for 

information.

United States Department of Agriculture • Animal and Plant Health Inspection Service • Safeguarding American Agriculture

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of Civil Rights, 1400 Independence Avenue, S.W., Washington,

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