These ants get their common name from their ability to inflict
especially painful bites and stings. The two most important
species are the southern fire ant (Solenopsis xyloni McCook)
and the red imported fire ant (Solenopsis invicta Buren).
The southern fire ant is a native species and ranges from
California to southern South Carolina to northern Florida.
The red imported fire ant is from central Brazil and is found
in the southeastern United States, from Virginia through Texas.
Workers polymorphic, about 1/16-1/4" (1.6-6 mm) long;
queens average 1/4" (6.6 mm) long. Head and thorax yellowish
red and abdomen black; reproductives darker. Antenna 10-segmented,
with 2-segmented club. Thorax lacks spines, profile unevenly
rounded. Pedicel 2-segmented. Stinger extruded in most alcohol-collected
specimens; readily inflict painful stings.
of the mandible and petiole (1st node of pedicel) will separate
these 2 species. The mandible of S. xyloni has 3 distinct
teeth on its inner/biting surface whereas, those of S. invicta
have 4 teeth and the petiole of S. xyloni has a ventral tooth
near the node's attachment to the thorax whereas, S. invicta
lacks such a tooth.
(1) Fire ant (Solenopsis geminate) with ridge on lower front
margin of mesothorax having 1 or more teeth, 1st node in profile
with rear margin almost straight. (2) Little black ant (Monomorium
minimum) with antenna 12-segmented, club 3-segmented. (3)
Acrobat (Crematogaster spp.), big-headed (Pheidole megacephala),
harvester (Pogonomyrmex spp.), and pavement (Tetramorium caespitum)
ants have spines on upper surface of thorax; in addition acrobat
ants with heart-shaped abdomen and pedicel attached to upper
surface of abdomen, big-headed ants with soldier with head
very large and 3-segmented antennal club, harvester ants with
underside of head with a brush of long bristles (coarse hairs/setae
called psammophores), and pavement ants with head and thorax
covered with distinct ridges. (4) Other small dark ants have
For the red imported fire ant, single-queen mounds usually
number 30-100/acre (0.4ha) with typically 80,000 but up to
250,000 individuals per colony. Multiqueened colonies may
number 200-700/acre (0.4ha) but contain fewer individuals
per colony, and there is less fighting between the colonies.
Typical mounds are rounded, being up to 18" (48 cm) high
and 24+" (61+ cm) in diameter, each with several tunnels
just under the soil surface extending out several feet. A
queen in a large colony is capable of producing her own weight
in eggs each day or about 1,500 or more. Developmental time
(egg to adult) for workers ranges from 22-38 days. A mature
colony can produce as many as 4,500 swarmers during the year,
with 6-8 mating flights occurring between spring and fall.
Mating flights usually begin about 10 am, 1-2 days following
a rain if it is warm (about 75 degrees F / 24 degrees C),
sunny, and not very windy. Minor workers live 30-60 days,
intermediates (medial) 60-90 days, and majors 90-180 days
or longer. Queens live 2-6 years. Males die shortly after
mounds of the southern fire ant are flattened and irregular,
covering 2-4 sq ft (0.17-0.37 sq m). Swarms occur from May
through October in the afternoon to early evening of warm
days. Developmental time can require as few as 44 days. Its
biology has not been thoroughly studied.
Fire ants are typically ground-nesting ants. However, the
southern fire ant will sometimes nest in the wood or masonry
of buildings, especially in areas near the soil or warmth
such as fireplace hearths. When the southern fire ant nests
outside near a house, it is usually in the vicinity of the
kitchen. Outside nests are usually situated under stones or
other covering objects, or in the soil at the base of a tree
or shrub, or in clumps of grass.
red imported fire ant typically nests outside. Each colony
has its own territory, and there is usually no movement between
colonies. However, they will sometimes nest in areas of exposed
soil within buildings such as bath traps. They also have the
habit of building outside nests adjacent to foundation walls.
They are commonly introduced into new areas via potted or
balled shrubs and trees.
ants are attracted to electrical junction boxes of traffic
signals, air conditioners, etc. When they mass around the
electrical contact points, they cause the equipment to malfunction.
They will also nest in gas and water meter boxes and then
follow the pipes into the building.
ants prefer food with a high protein content but will feed
on almost anything, plant or animal. The southern fire ant
has been known to remove insulation from phone and electrical
wires, and to gnaw on clothing, especially if soiled. They
usually feed on seeds, insects, young tree bark, honeydew
and other sweets, preferring oily meats and nuts.
imported fire ants are particularly destructive to vegetation.
Workers forage in established trails.
Fire ant control is difficult. It usually requires repeated
applications of liquid or granular residuals to eliminate
the colony. Particularly effective with a single application
are residual aerosols applied under high pressure (160 psi)
with a long injection probe.
baits are slower acting, they are effective. Baits containing
only a stomach poison require several applications each season
to control newly emerging workers when the queen(s) is/was
not killed, and new colonies. Baits containing only an insect
growth regulator can provide year-long control with 1 or 2
applications in the residential situation when followed in
7-10 days with a liquid residual application to kill the active
foragers. Newer baits containing avermectin,, which acts as
both an insect growth regulator and slow-acting stomach poison,
give good control without liquid application.