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Los Angeles County West Vector & Vector-Borne Disease Control District
Red Imported Fire Ant
The red imported fire ant (Solenopsis invicta), is an introduced species from South America. It is well known for its aggressive nature when disturbed. It can inflict a painful sting causing a burning sensation, hence the name "fire" ant. Red imported fire ants (RIFA) can harm people and native wildlife, cause damage to buildings and electrical equipment, as well as interfere with harvesting and maintenance of pastures and crops.
Biology
The RIFA build mounds in a variety of soil types but seem
to prefer open, sunny areas. Mounds can reach 18 inches in height.
They can also establish colonies in rotting logs, around stumps and trees, and
in or under buildings.
The average colony contains up to 500,000 workers,
several hundred winged ants and one or more queens. The ants can vary in
size from around 1/8" to 1/4" in length (see picture
below).
Worker ants are wingless, sterile females. They care
for the queen and brood, forage for food, and protect the colony from
intruders.
The winged ants are reproductives and live in the mound until
their mating flight. Mating flights are most common in the spring and
fall, soon after a rainy period. Males die soon after mating, while
the fertilized queen looks for a suitable nesting site. There she will
shed her wings and begin digging a chamber in which to start a new colony.
The new queen lays about a dozen eggs. When they hatch
7 - 10 
days
later, the larvae are fed by the queen. Larvae develop in to pupae in 6 -
10 days. Adults emerge from pupae in 9 - 15 days. Later, when
the queen is cared for by the workers she can lay up to 800 eggs a day.
The queen can live seven years or more while the workers usually live about five
weeks.
Distribution
These ants were first introduced to the United States in
approximately 1930 in the state of Alabama. The red imported fire ant is
now established over much of the Southeast. All counties in Alabama,
Florida and Louisiana are infested. Counties in Arkansas, Georgia,
Mississippi, Oklahoma, North Carolina, South Carolina, Tennessee, and Texas plus
Puerto Rico have been invaded. Isolated colonies have been found as far west as
California, and as far north as Kansas City, Missouri.
RIFA were officially detected in Los Angeles and Orange
Counties in November of 1998. It is believed that they have been present since
at least 1996. The ants are expected to colonize irrigated agricultural
areas and lawns throughout California.
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Health Risk
Fire ants are aggressive and will defensively
attack anything that disturbs them. They can sting repeatedly. After
firmly grasping the skin with its jaws, the fire ant arches its back as it
inserts its stinger into the skin, injecting venom. It then typically
inflicts an average of seven to eight stings in a circular pattern.
Symptoms of a sting include burning and itching, which
usually subsides within 60 minutes. This is followed by the formation of a
small blister at the site of each sting within a few hours. In addition, a
white pustule forms at the sting sites in a day or two. Infection can
occur if the pustule is scratched or broken.
Although the stings are not usually life threatening, they
are easily infected and may leave permanent scars. On rare occasions,
anaphylaxis (a generalized, systemic allergic reaction to the stings) can
occur, and may be life threatening. It usually occurs in persons
sensitized by a previous sting. Signs of anaphylaxis may include flushing,
general hives, swelling of the face, eyes, or throat, chest pains, nausea,
severe sweating, loss of breath or slurred speech. If this occurs, the
person should immediately seek emergency medical assistance!
If you think you have discovered red imported
fire ants or have questions regarding this pest,
Call the
California Department of Food and
Agriculture toll free at:
1 (888) 434-7326