Fire Ant Morphology, Reproduction, and Development

Imported Fire Ants November 17, 2015 Print Friendly and PDF

If it were it not for the painful experiences associated with fire ants, most people might find these creatures fascinating. Their life cycle and social behavior are surprisingly complex.

Habitat:  Fire Ant Colony

Fire ants live in colonies in nests in the soil. The above ground mound of soil is just a small part of the fire ant nest (see How Tall Do Fire Ant Mounds Get?). The below ground 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 within their nests (mounds) both horizontally and vertically to optimize access to favorable 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.


Life Cycle:  How does a colony become a colony?

Winged male and female fire ants. By Bart Drees.

Winged males and females (called alates) fly hundreds of feet up from the ground and then mate in flight.

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.

Males die soon after mating.

Once mated, the female lands, breaks off her wings, and searches for a place to establish her new colony, of which she is now queen.

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 about 25 eggs

After these eggs hatch the queen feeds them from energy from her digested wing muscles and cannibalized eggs.  She never leaves the colony again.

After a month or two these developing ants emerge as tiny worker ants called minims.  These first worker ants assume the job of caring for the queen and developing ants.

Visible mounds appear above the turf surface as the colony increases in size, usually within several months.

A fire ant queen can lay eggs that are fertilized or unfertilized with sperm that she has stored in her body since mating:

  • Unfertilized eggs develop into winged male fire ants.
  • Fertilized eggs develop into sterile female worker ants or into fertile winged females.

Developmental stages of fire ants are 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). VIDEO: Worker ants tending brood.

 

Fire ant larvae that receive more food become winged females instead of workers. Winged fire ants, called winged sexual reproductives,  are produced throughout the year, but are most common in spring (April through June). VIDEO: winged sexual reproductive male and female ants

Single queen fire ant colonies (monogyne colonies) have a one fertile queen that lays all the eggs in the colony.

Multiple queen fire ant colonies (polygyne colonies) have multiple fertile queens that share egg laying and colony leadership.

The queen influences the colony by secreting chemicals called pheromones.  VIDEO: fire ant queen

A fire ant queen can live for 7 years and produce as many as 1,000 eggs per day

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.


Social Structure:  Roles within the colony

Worker ants build the mound, care for the queen and brood (eggs, larvae and pupae), 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.  VIDEO: Worker ants tending brood.

Nurse ants are younger workers that 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.

When a fire ant colony or mound is disturbed, worker ants rush to the surface to defend the colony by biting and stinging while the queen(s) quickly crawl downward to avoid harm.  See VIDEO: Disturbed laboratory colony.

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.


Feeding: A communal system

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.

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. 


Why Fire Ant Control Products Don't Provide a Permanent Solution

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.

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 baits usually can give 6 to 18 months of control.
  • 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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USDA / NIFA

This work is supported by the USDA National Institute of Food and Agriculture, New Technologies for Ag Extension project.