Fire Ant Control: What’s Being Done About It?

Scientists in several southeastern states wonder whether a tiny fly that beheads its victims can keep fire ants in their place.

The phorid fly, about the size of an ant’s head, lays its eggs inside of the fire ant’s body. The larvae develop in the ant’s head, and when they hatch, they decapitate the ant.

Off with its head, one might say, quoting a popular children’s book.

red imported fire ant mound

Red imported fire ant mound

Most people think of fire ants as the red, stinging pests that live in huge mounds and attack in swarms. Those ants—named Solenopsis invicta—are only one of 20 different species of fire ant. Solenopsis invicta, or the red imported fire ant, is the most aggressive of all fire ant species, and also the most widespread.

Two imported fire ant species and four native species live in North America. The imported species include:

  • Red imported fire ants, introduced to this country after they hitched a ride on a cargo ship and landed in Mobile, Alabama in 1933. Since then, they have spread throughout the southern region and are a worldwide pest. They are very common in South America, where the name for them is translated as “off with your pants.”
  • Black imported fire ants (S. richteri), introduced through the port in Mobile, Alabama in 1918. Black imported fire ants are less aggressive than their red counterparts, and they have remained localized in northeast Mississippi, northwest Alabama and a few southern counties in Tennessee. Although the two imported species are interbreeding, the red imported fire ants or the hybrid are displacing S. richteri in many areas.
Red imported fire ants

Red imported fire ants

In addition to displacing other ant species from an area, the red imported fire ant leads to a reduction or elimination of field mice, snakes, turtles and other vertebrate species (IPM World Textbook).

Native fire ants species include:

  • Tropical fire ants (S. geminata) are now a worldwide species thanks to global commerce. Like S. invicta, this species is aggressive in its sting and also can damage crops. However, it is susceptible to other ant species. (My references indicated this spp was introduced from the Carribean and northern South America, though, like you, I have heard it referred to as a native.)
  • Desert fire ants (S. aurea and S. amblychila), found in the desert areas in western Texas, are yellowish red to reddish yellow.
  • Southern fire ants (S. xyloni) resemble the red imported fire ant in physical characteristics; however, they are slightly smaller and less aggressive (but not less painful when they sting). The two species can usually be differentiated under microscopic examination.

Fire ant stings, although not usually life-threatening, are intensely painful. The burning sensation at the sting site, accounting for the fire ant’s name, precedes the emergence of red and white pustules. Fire ants typically attack in large numbers (I think of mating flights when I think of swarms), and each ant can sting repeatedly, even after its poison sac is empty. (eXtension fire ant site)

Until the late 1990s, insecticide drenches and broadcast mound baits were the only known control for fire ants. Although they were both effective at killing the majority of the population, only treatments that went deep into the mound killed entire colonies. Often the queen, who lives deep underground, would escape and begin a new colony elsewhere. The queen can live up to seven years and lay as many as 1600 eggs per day during her lifetime (IPM World Textbook).

Many environmentally-concerned people have been searching for non-chemical controls for fire ants; however, scientific trials with many of them have not proven their effectiveness, and some are actually dangerous. These “home remedies” include:

  • Club soda
  • Grits
  • Gasoline
  • Flooding
  • Dish detergent
  • Setting fire to the mound

None of these remedies are recommended or have been proven to be effective at reducing fire ants. Some combinations of organic treatments, however, have been shown to have some effectiveness.

Phorid fly over ant

Phorid fly over ant

During the past decade, scientists have been exploring two biological control options for imported fire ants (we have phorids collected from both the black and red that were released here to place them on the same species they were attacking in S. America). One, the phorid fly, is currently the most effective, and several species of flies have been released en masse in several southern states, including Texas and Alabama. In fact, a few years ago in Texas, wildlife management agencies encourage farmers and ranchers to take ants from their property to a location rich in phorid flies, and then bring the ants, with phorid eggs embedded, back to the mounds.

For an explanation of how to identify phorid flies, see Mike Merchant’s Insect in the City blog.

Researchers in Florida are also exploring parasitic microsporidiaKneallhazia solenopsae, Thelohania solenopsae and Vairimorpha invictae—to infect the ants. One possibility is to infect the phorid flies with the pathogens and use them to infect the ants. According to USDA Agricultural Research Service scientist David Oi, K. solenopsae reduces colony founding by reproducing ants, affecting the survival of queens and hastening the death rate of colonies. The pathogen is harmless to phorid flies.

Homeowners and school personnel raise the most concern about fire ants because mounds often appear in backyards and playgrounds. To avoid the risk of being stung and to protect children from fire ant stings, several Web resources are available that detail how to identify fire ants and fire ant mounds and what to do if you find them:

2 Responses

  1. Fire ants are very common around here. If bad enough, appropriate measures must be taken to rid yourself of these pests.

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