INTRODUCTION
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.
RECOGNITION
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. Characteristics of the mandible and petiole (lst 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.
SIMILAR GROUPS
- Fire ant (Solenopsis geminata) with ridge on lower front margin of
mesothorax having 1 or more teeth, lst node in profile with rear margin almost straight.
- 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.
- Other small dark ants have 1 -segmented pedicel.
BIOLOGY
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. Multi- queened
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'F/24'C), sunny, and not very windy. Minor workers live 30-60 days, intermediates
(medias) 60-90 days, and majors 90-180 days or longer. Queens live 2-6 years. Males die
shortly after mating.
Typical 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.
HABITS
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.
The 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. Fire 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.
Fire 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 gnaw on clothing, especially if soiled.
They usually feed on seeds, insects, young tree bark, honeydew and other sweets,
preferring oily meats and nuts. Red imported fire ants are particularly destructive to
vegetation. Workers forage in established trails.
