Fire Ants

Scientific Name: Solenopsis spp.
CLASS/ORDER/FAMILY: Insecta/Hymenoptera/Formicidae
METAMORPHOSIS: Complete

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 (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.

Life Cycle

Colonies of crazy ants are moderate to very populous. The colonies may raise sexuals at any time of the year in warmer regions, but in the seasonal climate of north Florida, alate production is apparently limited to the warm rainy months of May through September (Trager 1984). On warm, humid evenings, large numbers of males gather outside nest entrances and may mill about excitedly. Workers patrol vegetation and other structures nearby. Periodically, a dealate queen emerges. Mating was not observed, but Trager (1984) suggested that it occurred in such groupings around the nest entrance. Wings of queens are removed while still callow and males were never observed to fly or use their wings in any way. However, in several cases it has been observed that males frequently appear at lights (Trager 1984).

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. 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 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.

Nest Sites

The crazy ant is highly adaptable, living in both very dry and rather moist habitats. The crazy ant often nests some distance away from its foraging area. It nests in such places as trash, refuse, cavities in plants and trees, rotten wood, in soil under objects and also have been found under debris left standing in buildings for long periods of time (Smith 1965). These ants can nest in a variety of locations from dry to moist environments. A crazy ant nest site can be found by looking for workers carrying food back to the nest.

Management

Non-chemical control is based on exclusion through good housekeeping practices and cleanliness eliminating food sources. Crazy ants nest outdoors so prevention of their entrance by caulking exterior penetrations and weather-stripping may aid in their control. Indoors chemical controls are based on baits, dusts, and spot treatments with residual sprays. Outdoor treatments include chemical formulations as baits, granules, dusts, and sprays. Read and follow label instructions and precautions before using any insecticide.

Control

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.Although 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.