Fire Ant


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 (RIFA; 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, introduced between 1933 and 1945, is from central Brazil and is now found in the southeastern United States, from Virginia south through Florida and westward through Texas, in southern New Mexico, southern California, and also in Puerto Rico. It is periodically found in other areas of the United States, usually associated with nursery stock. In 2006, the USDA reported that the RIFA exceeded $6 billion-a-year in damage and control costs.


Workers polymorphic, about 1/16-1/4″ (1.6-6 mm) long; queens average 1/4″ (6.6 mm, but up to 8 mm) long. Head and thorax yellowish red and abdomen black; reproductives darker with males black. 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, clypeus (upper lip), 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. The petiole of S. xyloni has a ventral tooth near the node’s attachment to the thorax whereas, S. invicta lacks such a tooth. In addition, the clypeus of S. invica has 3 small but distinct teeth or projections whereas, the clypeus of S xyloni has only 2 such teeth.

Similar Groups

    1. Fire ant (Solenopsis geminata) 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 ant (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 1-segmented pedicel.

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For the red imported fire ant, single-queen (monogyne) mounds usually number 30-100/acre (0.4ha) with typically 80,000 but up to 250,000 individuals per colony. Multi-queened (polygyne) 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. Single-queen colonies are territorial and reproduce by swarming whereas, multi-queened colonies are not territorial and reproduce by both swarming and budding. A queen in a  large  monogyne  is capable of producing her own weight in eggs each day or about 1,500 or more; polygyne queens produce fewer eggs. Developmental time (egg to adult) for workers ranges from 22-38 days. After founding, a colony can mature (become capable of producing swarmers) in 1 or 2 years. Mature colonies can produce as many as 4,500 swarmers during a 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.


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. 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. When exposed to flooding, the displaced colony will form a ball and raft the flood waters until it encounters dry land. Such ants typically arrive hungry and with a defensive attitude (they inject higher doses of venom), probably because of their vulnerability due to a lack of protection normally afforded by their nest.

Attacks on non-responsive residents (usually the elderly or infants) of health-care or extended-care facilities typically occur in the morning, following a heavy rain and/or flooding. The displaced ants usually gain entrance into the structure through the HVAC system, such as wall A/C units. Typically, they enter seeking food. Several such incidents have resulted in the death of the person receiving multiple stings. In addition, about 1-2% of the United States population is thought to be at risk of anaphylactic shock when  stung.

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. The attraction comes from one or more ants getting an electrical shock by completing the circuit. The shock stimulates the release of the defensive or under-attack pheromone, which attracts more ants, etc. 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 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. Red imported fire ants are particularly destructive to vegetation. Workers forage in established trails.

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Ants Pest Control Naples

Fire ant control is difficult. Elimination from a single property is possible for up to a season, but scheduled inspections and retreatment will be required because of periodic reinvasion. There are presently about 5 control choices. It should be noted that when using baits, with one exception, they should be applied when the ground is dry and no rain is expected for 24 hours. Also, they should not be applied in the heat of the day when than ants are not actively foraging; late afternoon is usually best.

  1. Individual mound injection. This involves a thorough inspection to locate each mound and then treating each mound with a termite rodding tool hooked up to a termite or similar rig. It is a quick kill for the mounds treated, but the many small mounds will be missed. This means multiple treatments over the season.
  2. Broadcast application with the 2-step method. This consists of a broadcast application with slow-acting bait, and then waiting 5-10 days for it to be distributed within the colony. Then individual mounds are treated with a fast-acting liquid, dust, or granules (must be watered in) to kill most of the remaining ants. One or 2 applications are required each year.
  3. Broadcast treatments with several applications per year. These applications involve baits that contain both an IGR and faster-acting pesticide. The slower the action, the longer the period between applications.
  4. Broadcast application with the quickest kill. One of the newer baits on the market will give control in about 2-3 days. A second application may be required in 3-4 months. Best used when the ants must be eliminated in a hurry around sensitive accounts.
  5. Broadcast application with one treatment per year. One bait on the market usually requires only one application each year, but must be watered in to achieve control in 2-3 days. It can be applied just before or after a rain. This tends to cost more, but requires fewer applications.
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