If it were not for the painful experiences associated with fire ants, almost anyone would find them fascinating. Their life cycle and social behavior are surprisingly complex.
Fire ants live in colonies in the soil. The aboveground mound of soil is just a small part of the fire ant nest. The belowground portion of the colony can extend from 1 to 3 feet deep.
Fire ant nests have tunnels that can extend as deep as the water table, thereby providing a source of moisture for the colony even during hot, dry summer months. Nests also have foraging tunnels near the surface that may extend many feet from the mound. Fire ants use these tunnels to search for and retrieve food.
Fire ants can move their nests both horizontally and vertically to optimize temperature and humidity. During extreme heat and drought, the ants go deeper into the ground, and mounds may lose their domed appearance. This behavior explains why mounds are often not seen during the hotter, dryer months. On the other hand, mounds are built up after rain and therefore are more obvious during rainy seasons.
Single queen fire ant colonies have a single fertile queen that lays all the eggs in the colony. The queen influences the colony by secreting chemicals called pheromones. Multiple queen fire ant colonies have multiple fertile queens that share egg laying and colony leadership. A fire ant queen can live for 7 years and produce as many as 1,000 eggs per day. You may see the term monogyne used to refer to colonies with a single queen, and the term polygyne to refer to colonies with multiple queens.
A mature colony can contain up to 400,000 sterile female worker ants. These ants range in length from 1/16 to 3/16 inch (1.5 to 5 mm) and are dark reddish brown with black abdomens. Worker ants build the mound, care for the queen and brood, defend the colony, and forage for food. Their functions within the colony are determined by the size and needs of the colony and by the ages of the worker ants. The younger workers serve as nurse ants which tend and move the queen and brood. Older workers serve as reserves to defend the colony, and construct and maintain the mound. The oldest worker ants become foragers.
The adult worker ants normally live about 60 to 90 days. In the summer, worker ants live about 35 days. However, in the cooler parts of the year, workers can live for months. Worker ants can roam far from the nest in search of food, such as other insects, decaying plant and animal material, and plant seeds. Plant nectar is also a food source.
Developmental stages include eggs, larvae, and pupae (collectively referred to as brood). Eggs are spherical and creamy white. Larvae are legless, cream-colored and grub-like, with distinct head capsules. Pupae resemble worker ants and are initially creamy white, turning darker before adult ants emerge (eclose).
Fire ants have a communal system of feeding. The workers in charge of food gathering carry the food back and share it with the rest of the colony. Fire ant workers feed liquid foods to other ants in the colony by regurgitating liquids from their crops, a process called trophallaxis. However, they have a sifting structure in their throats that prevents them from swallowing solid food. Fire ant workers have to carry solid food back in their mouths and then feed the particles to the oldest fire ant larvae. These larvae externally digest the food using special digestive enzymes. Once the food is digested, the worker ants can take the food byproducts from the larvae and share them with the rest of the colony.
A fire ant queen can lay eggs that are fertilized or not fertilized with sperm that she has stored in her body since mating. If the queen lays an unfertilized egg, it develops into a winged male fire ant. Fertilized eggs develop into sterile female worker ants or into fertile winged females. Fire ant larvae that receive more food become winged females instead of workers. Winged fire ants are produced throughout the year, but are most common in spring (April through June).
Mating flights occur most often when the temperatures are between 70 and 95 degrees F., when there is low wind and high humidity, and usually within 24 hours of a rain. The winged males and females fly hundreds of feet up from the ground and then mate in flight. Males die soon after mating. Once mated, the female lands, breaks off her wings, and searches for a place to establish her new colony. Many newly mated fire ant queens are eaten by predators such as spiders, lizards, dragonflies, other ants, and ground beetles. Those queens that survive dig small chambers in the soil, where they lay a few eggs. These first eggs hatch and mature into workers that care for the queen and the next brood of larvae. Visible mounds appear above the turf surface as the colony increases in size, usually within several weeks or months.
Fire ant control products are often criticized because they control fire ants for a while, and then the fire ants come back. The lack of permanent control relates to fire ant biology. There will always be new, winged fire ant queens looking for somewhere to start new colonies. Newly mated queens can often fly surprising distances. This means that newly treated zones can be reinfested even from long distances. In a fire ant infested area, fire ant workers from local colonies can kill more than 99 percent of new fire ant queens. A queen is most likely to succeed in an area where all the other fire ants have been eliminated. Fire ant baits usually can give 6 to 18 months of control.
There are several other reasons why fire ants come back. Some fire ant control methods kill many fire ant workers, providing temporary relief. However, the queen can produce more workers that will rebuild the colony. If a fire ant mound redevelops in a few weeks, this may be the case. Fire ant control strategies that rely on treating every mound will also frequently miss the very small colonies, consisting of the queen and relatively few workers. With the larger colonies no longer competing for food, these small colonies can grow rapidly.
Fire ants, like other insects, are cold-blooded animals. This means that they cannot maintain their body temperatures by internal mechanisms the way warm-blooded animals can. Their body temperatures and functions depend on the outside temperature. Thus many of the recommended treatment strategies are slower or less effective during cooler months.
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