“The ants go marching one by one, hurrah, hurrah…”

Actually, if this song were about red imported fire ants, the lyrics would say “go stinging one by one.” Fire ants sting humans by sinking their mandibles into the skin and swinging their abdomens around to inject venom. This venom serves a purpose: when used against prey, it can kill or paralyze. When injected into humans, the toxic alkaloids produce an immediate burning sensation at the entry site. A swelling soon appears and a blister forms. Within a short amount of time, the blister fills with pus. Venom begins to break down cells and tissues. Reaction to the venom may include nausea and vomiting, disorientation, dizziness, asthma and anaphalaytic shock. Usually the sting simply gets itchy and irritated. Less than 5% of people stung experience systemic anaphylactic reaction, which can be fatal.

No wonder it sounded like a good idea when Congress initiated a cooperative federal and state program in 1957 to eradicate red imported fire ants from 126 million acres…at a cost of $200 million over a 12-year period.

Taxonomy

Class: Insecta
Order: Hymenoptera
Family: Formicdide
Genus and Species: Solenopis invicta

Origin

Originally from tropical South America, the red fire ant gained entry to North America through cargo ships in the port of Mobile, Alabama in the late 1930s. It immediately began to thrive in its new location, and colonies spread quickly. The first colony was discovered in 1942, when 13-year-old Ed Wilson came across a mound in the empty lot next to his home. He continued to study red fire ants while attending college. While Wilson continued his observation, the ants continued to spread throughout the southern U.S. By 1975, the red imported fire ant had colonized over 52 million hectares of the United States.

The most common species of fire ants is Solenopsis invicta (S. wagneri), which is also the most aggressive. There are four different classes of red imported fire ants that live in a colony: winged males, winged females, workers, and queens. The North American red imported fire ant is unique in that it forms colonies with multiple queens.

Work, Work, Work

The red imported fire ant’s life is extremely organized. Every ant has a job to do. They go about doing it day after day without stopping. The worker’s job is to keep the larvae, pupae, and queen clean. Cleanliness appears to be extremely important to the ants. They are constantly cleaning the larvae, the pupae, the queen, and the colony. Workers also forage to find food for the colony.

The red imported fire ant has two stomachs: one for its own food supply, and one for the colony’s food supply. The second stomach is called a crop. The ants feed mostly on other insects but also attack small birds and other invertebrates. They especially like to eat soft fruits. Flea larvae, chinch bugs, cockroach eggs, ticks, and other insects are also on their menu.

The winged females go on mating flights and found new colonies. The male’s only job is to mate with the queen. Soon after mating, the male will die.

Red fire ants migrate from one site to another quite often. A young queen only needs half a dozen ants and one day to build a new colony. These ants will build mounds in any type of soil and even indoors. In three months, a new nest could contain over 300 workers. Within a year, with multiple queens at work, the nest will contain over 11,000 individuals. At the end of three years, a staggering 50 to 60 thousand ants will have built a multichambered mound about three feet high. The ant pictured is a female worker. Her job is to find food for, and help clean, the colony.

Troublemakers

Fire ants can cause quite a problem. Red imported fire ants disrupt farming production because they construct their colonies on precious farmland. Farm machinery is often damaged by running over a mound. These can quickly strip fruit trees of their fruit. And because they like to make their mounds in sunny areas, many pastures are heavily infested. Their effect on pastures, hay fields, and recreational turf grass is at least a $28 dollars per acre expense.

Fire ant stings can injure and even kill livestock and poultry. Small birds such as baby quail are fair game to the expanding colony. Worse yet , they pose a threat to humans.  In 1987 in South Carolina, 500,000 stings required medical attention, costing $1.8 million. The ants appear to be attracted to electromagnetic fields and attack electrical insulation or wire connections. Along with damage to electrical equipment, they are a danger to workers and can cause electrical shorts and fires.

The Mirex War

Attempts to stop this ever advancing insect involved the use of various insecticides. Mirex was developed by Allied Chemical Corporation and used extensively in the war on fire ants. By 1967, the National Academy of Sciences had gathered data indicating Mirex was producing substantial negative effects on chickens, fish, baby rats, and especially crabs and other crustaceans. The use of Mirex was subsequently banned. By 1976, when the ban on the use of Mirex had taken effect, the U.S. government had spent over $91.5 million on eradication efforts.

There is still a great deal of concern regarding the spread of the red imported fire ant. Competition with native ants has the potential of limiting its range. The best barrier, however, may be cold weather. One big question remains: can the red Imported fire ant breed with native ants and acquire a capacity to endure cold weather?

Sources
http://www.uaex.edu/natural/fireant/biology.htm
http://fireant.tamu.edu
http://www3.sk.sympatico.ca/brucda/980504.htm
http://www2.ncsu.edu/unity/lockers/project/pestmngt3/AG268/html/fire_ants.htm
http://entweb.clemson.edu/cuentres/eiis/newimp/ni1.pdf