The red imported fire ant (Solenopsis invicta), is an introduced species from South America.  It's well known for its aggressive nature when disturbed.  It can have a painful sting causing a burning sensation.  Red imported fire ants (RIFA) can harm people and native wildlife, cause damage to buildings and electrical equipment, as well as interfere with harvesting and maintenance of pastures and crops.

Biology   

Red imported fire ants live in colonies that contain cream-colored to white immature ants, often called brood. The brood is the eggs, larvae, and pupae. Also within the colonies are adult ants of different types, or castes. The castes include winged males, winged females (which are unmated queens), workers, and at least one queen. The winged males and females fly from nests in the spring to early summer to mate. Upon landing, mated females will shed their wings after finding a nesting site, while the males die. Thousands of winged males and females can be produced every year in large colonies, do'nt sting, and fewer than 10% of the females will survive to produce a colony. Newly mated queens can fly 12 miles from the nest or even farther in the wind, but most land within a mile.

New colonies do not make conspicuous mounds for several months. Once a colony is established, a single queen can lay over 2,000 eggs a day. Depending on temperature, it can take 20 to 45 days for an egg to develop into an adult worker. Workers can live as long as 9 months at 75°F, but life spans usually are between 1 and 6 months under warmer outdoor conditions. Queens live an average of 6 to 7 years.

Fire ants are omnivorous feeders, feeding on carbohydrates, proteins, and lipids. Their food preferences change depending on the nutritional requirements of the colony. In the spring and summer, the colony produces new offspring and the protein needs of the colony increases. Adult ants require carbohydrates and/or lipids to sustain themselves throughout the year. Solid protein based foods are liquified by placing them on a depression in front of the mouth of the oldest larvae (the fourth instar stage), and then vomit digestive enzymes onto the food. Once liquified, the fourth instar larvae suck up the protein and vomit for the workers, who pass it on to the rest of the colony.

Workers will forage for food more than 100 feet from the nest. They generally forage when the air temperature is between 70° and 90°F. When a large food source is found, fire ants recruit other workers to take the food back to the colony. Liquids are eaten at the food source, and stored until it's vomited for other ants in the colony. Liquids from solid foods are extracted at the source or are carried back as solid particles. Large solids can be cut into pieces to be carried back to the colony.

There are two types of fire ant colonies: the single-queen, or monogyne, colonies, and the multiple-queen, or polygyne, colonies. Single-queen colonies have only one egg-laying queen, and contain as many as 100,000 to 240,000 workers. Multiple-queen colonies have many egg-laying queens (usually 20 to 60), with 100,000 to 500,000 workers. Single-queen colonies fight with other fire ant colonies. Because of this antagonistic behavior, colonies are farther apart, resulting in a maximum of 40 to 150 mounds per acre. Multiple-queen colonies generally do not fight with other multiple-queen colonies. Consequently, mounds are closer together, and can reach densities of 200 to 800 mounds per acre. Multiple-queen mounds may also be inconspicuous, often times being clusters of small, flattened excavations, in contrast to the distinct dome-shaped mounds of single-queen colonies. Workers from single-queen colonies range in length from 1/8 to 1/4 in, and are usually reddish brown to black. Workers of multiple-queen colonies are generally smaller (1/8 to 3/16 in), have only a few large workers, and are lighter in color (orangish-brown) than single-queen colony workers.

The large colony sizes and numerous queens makes multiple-queen colonies harder to eliminate than single-queen colonies. Since 1973, multiple-queen colonies have been found in eight of the 11 fire ant infested states. Multiple-queen colonies have fewer winged, or alate, queens that will start new colonies after a mating flight than single-queen colonies. However, multiple-queen colonies can establish new colonies by budding, where a portion of the queens and workers splits off from a colony.

The spread of fire ants into new areas depends on climate, surrounding fire ant populations, native predators, and the competitors in the area. Areas with an abundance of natural enemies and competing ant species may slow colony establishment because the enemies prey on newly-mated queens and compete for resources. However, if an area is disturbed, for example, by clearing land for pastures or urban development, natural enemies or competitors may be hurt and fire ants may colonize the area better.

It can take as long as 11 years for single-queen fire ant colonies to become the dominant ant species in a new area which has been disturbed by urbanization, and has not been treated with insecticides to control ants. Multiple-queen colonies may become dominant in new areas at a slower rate because they spread more by budding than by establishing numerous new colonies scattered throughout an area after mating.

In areas where native ants and fire ant populations are reduced or gone from insecticides, reinfestation may be noticeable within a month after treatment. Fire ants infest these areas more and compete with other ant species because of their reproductive capacity and faster colony development. If fire ant control isn't maintained, the reinfestation of an area can have higher fire ant populations than before the insecticides.

The RIFA builds mounds in a variety of soil types but seem to prefer open, sunny areas. They can also establish colonies in rotting logs, around stumps and trees, and in or under buildings. The average colony contains 500,000 workers,  several hundred winged ants and one or more queens. Ants are 1/8" to 1/4" in length. Worker ants are wingless, sterile females and care for the queen and brood,  forage for food, and protect the colony. The winged ants are reproductive and live in the mound until they mate.  Mating flights are mostly in the spring and fall, after a rainy period.  Males die after mating, while the fertilized queen looks for a nesting site where she will shed her wings and begin digging a chamber to start a new colony. The new queen lays about a dozen eggs. When they hatch 7-10 days later, the larvae are fed by the queen. Larvae develop in to pupae in 6-10 days and Adults emerge in 9-15 days. When the queen is cared for by the workers she can lay up to 800 eggs a day.  The queen can live seven years or more while the workers usually live about five weeks.

Distribution

These ants were first introduced to the United States around 1930 in Alabama. The red imported fire ant is now in much of the southeast and Puerto Rico. Isolated colonies have been found as west as California, and as north as Kansas City, Missouri. RIFA were found in Los Angeles and Orange County in November 1998. It's believed that they have been there since at least 1996 and are are expected to colonize throughout California.

Health Risk

Fire ants are aggressive and will attack anything that disturbs them by stinging. After firmly grasping the skin with its jaws, the fire ant arches its back as it inserts its stinger into the skin, injecting venom. It then typically inflicts an average of seven to eight stings in a circular pattern. Symptoms of a sting include burning and itching, which is gone in 60 minutes. This is followed by a small blister at the site of each sting within a few hours, and a white pustule forms in a day or two.  Infection can occur if the pustule is scratched or broken. Although the stings aren't usually life threatening, they are easily infected and can leave permanent scars. On rare occasions, anaphylaxis can occur, and can be life threatening. Signs of anaphylaxis can include flushing, hives, swelling of the face, eyes, or throat, chest pains, nausea, severe sweating, loss of breath or slurred speech and requires emergency care.

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