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About Fire Ants

The red imported fire ant, Solenopsis invicta Buren, the black imported fire ant, Solenopsis richteri Forel, and their hybrid are nuisance insects and their stings can cause serious medical problems. Imported fire ants interfere with outdoor activities and harm wildlife throughout the southern United States. Ant mounds are unsightly and may reduce land values. In some cases, imported fire ants are considered to be beneficial because they prey upon other arthropod pests. In urban areas, fire ants prey on flea larvae, chinch bugs, cockroach eggs, ticks and other pests. In many infested areas, the problems outweigh the benefits and controlling fire ants is highly desirable. However, eradication of this species is not currently feasible (see History and Control Efforts). When deciding whether or not to control fire ants, one must weigh the benefits of fire ant control against the cost and environmental impact of control methods. Consideration of biological control of fire ants may not be compatible with some types of insecticide use. Insecticides are not always 100 percent effective, nor are most approved for use everywhere that ants occur. Insecticides are also expensive and potentially hazardous to the environment and other animals. Chemicals provide only temporary control of fire ants and must be reapplied periodically. Where applicable, you should select programs (for urban or agricultural areas) that use a combination of non-chemical and chemical methods that are effective, economical and least harmful to the environment.

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Identification

There are three types of Imported Fire Ant: the red imported fire ant (RIFA), Solenopsis invicta Buren, the black imported fire ant (BIFA), Solenopsis richteri Forel, and their hybrid (HIFA). All share common characteristics such as a ten-segmented antenna with a two-segmented club, and a two-segmented waist.

Ten-segmented antenna with two-segmented antennal club

Two-segmented waist


Variations in gaster color for the three types of fire ant

  • Hybrid fire ant gaster

  • Black fire ant gaster

  • Red fire ant gaster


The red has a dark gaster and the rest of its body is a lighter red. The black is darker at the end and has golden patch at the top of the gaster defined by distinct dark outlines. For the hybrid, the light patch on the gaster still exists, but the lines defining it are hazy and indistinct.

The first worker ants produced in a colony are small and are called minims. As the colony grows larger workers are produced, resulting in small (minor), medium (media), and large (major) workers.

Range of worker size

Imported fire ant in comparison with other common species

* Competitor Species

Fire Ant Look Alikes

Properly identifying the ant species is the first step in determining the need for control. Most homeowners recognize imported fire ants by the mounds they build, or the sting the ants inflict. However, there are other characteristics to look for. Their aggressive nature relative to other ant species is one such trait. Generally, hundreds of fire ant workers will swarm out of the ant mound when disturbed, and run up vertical surfaces to sting. If you are unsure of the ant species you have, contact your county Extension office for assistance with proper identification.


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Biology

Castes

Fire ants are social insects and unlike many insect pests, they are very organized. Red imported fire ant colonies consist of the brood and several types (castes) of adults. The whitish objects often found at the tops of the mounds are actually the ant's developmental stages—the eggs, larvae and pupae. Types of adults are:

  • winged males (distinguished from the females by their smaller heads)
  • red-brown (RIFA) or black or dark brown (BIFA and HIFA) winged females
  • one or more queens (wingless, mated females)
  • workers

Examples of fire ant

Worker ants are wingless, sterile females. They protect the queen by defending the nest from intruders, by feeding the queen only food that the workers or larvae have eaten first, and by moving the queen from danger. They also forage and care for the developing brood.

Newly Mated Queen

The winged forms, or reproductives, live in the mound until their mating flight, which usually occurs in the late morning and afternoon soon after a rainy period. Mating flights are most common in spring and fall. Males die soon after mating, while the fertilized queen lands and walks around to find a suitable nesting site, sheds her wings, and begins digging a chamber in which to start a new colony. Sometimes, several queens can be found within a single nesting site.

A newly-mated queen lays about a dozen eggs. When they hatch 7 to 10 days later, the larvae are fed by the queen. These larvae will develop into small worker ants that will feed the queen and her subsequent offspring. Later on, a queen fed by worker ants can lay from 800 to 1,000 eggs per day if needed. Larvae develop in 6 to 10 days and then pupate. Adults emerge 9 to 15 days later. The average colony contains 100,000 to245,000 workers and up to several hundred winged forms and queens. Queen ants can live 7 years or more, while worker ants generally live about 5 weeks, although large workers can survive much longer.

In addition to hybrid imported fire ants, there are two kinds of red imported fire ant colonies—the single queen and multiple queen forms. Workers in single queen colonies are territorial. Workers from multiple queen colonies move freely from one mound to another, which has resulted in a dramatic increase in the number of mounds per acre. Areas infested with single queen colonies contain 40 to 150 mounds per acre (rarely more than 7 million ants per acre). In areas with multiple queen colonies, there may be 200 or more mounds and 40 million ants per acre.

Mounds

Imported fire ants build mounds in almost any type of soil, but prefers open, sunny areas such as pastures, parks, lawns, meadows and cultivated fields. Mounds can reach 18 to 24 inches in height, depending on the type of soil. Often mounds are located in rotting logs and around stumps and trees. Colonies also can occur in or under buildings.

Colonies frequently migrate from one site to another. A queen needs only half a dozen workers to start a new colony, and can build a new mound several hundred feet away from their previous location almost overnight. Flooding causes colonies to leave their mounds and float until they can reach land to establish a new mound. Colonies also can migrate to indoor locations.

  • Mounds consist of many interconnected galleries and chambers
  • Galleries and chambers can extend as much as 30 to 40 centimeters down
  • There are a few deeper tunnels that can reach the water table
  • Lateral foraging tunnels can extend up to ten meters from the mound
  • Queen and brood are moved throughout the mound in response to temperature
  • On cold days, the colony moves deep into the mound. As the mound becomes warmer, the ants move closer to the surface

Foraging

  • A majority of fire ant foraging occurs between 72°F and 96°F
  • Foraging tunnels radiate underground from the mound. Fire ants exit the mound via these tunnels which may first open to the surface around 12 inches from the mound's edge
  • When small amounts of food are found workers return directly through the opening from which they came
  • When fire ants encounter larger pieces of food, ants leave pheromone trails as it returns to the mound with a sample of the food to recruit more ants
  • Fire ants are omnivorous, their main source of food are other invertebrates, but they also feed on plants, sap, honeydew and dead animals
  • Queens, workers and 1st-3rd instar larvae can only consume liquids
  • Oils are stored in the crop and post pharyngeal gland
  • Water soluble liquids are stored only in the crop
  • Liquids may be transferred several times between foragers before it is transferred to nurse ants and eventually to the queen and larvae
  • Solids greater than 0.88 microns are strained from liquids and formed into pellets by workers
  • Pellets and solid food are given only to fourth instar larvae which break down the solids and digest the proteins that are distributed to other larvae and queens
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Impact

Tennessee areas under the IFA quarantine have expanded during the last two decades and in 2009 cover more than 13.8 million acres or slightly more than 50% of Tennessee's land area. About 3.4 million Tennesseans or 56% of the state's population live in infested counties and are affected by these pests.

Human Medical Impact

Fire Ant Sting Symptoms and Treatment
    Treatment
Common Symptoms
  • Burning
  • Itching
  • White pustule in 24-48 hours
  • Treat stings with over the counter products to relieve insect stings
  • Do not scratch area because sting can be easily infected and leave permanent scar
Rare/Severe Symptoms
  • Sever chest pain
  • Nausea
  • Severe sweating
  • Loss of breath
  • Serious swelling
  • Slurred speach
  • Call 911 or go to emergency room

Precautionary Measures

  • Teach children and visitors about fire ants and their hazards
  • Wear protective clothing during outdoor activities
  • Treat stings with insect bite remedy that eases pain and protects against pain
  • Control fire ants in areas used most frequently by people and pets
  • Use insect repellents on clothing and footwear (the treatments can temporarily discourage foraging ants)
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History