Fire Ants

- A dangerous and invasive insect pest -

Summary: The red imported fire ant is a serious pest in pastures and lawns in the southern US and northern Australia. The ant is highly aggressive and has an extremely potent and painful sting.

Jack DeAngelis, PhD
OSU Ext. Entomologist (ret.)

Fire ants (Solenopsis spp.) are so named because of their painful sting, not their bite. Like wasps, which are closely related to ants, all ants have stingers. While some ants use their stingers in defense of the nest and to subdue prey, a few species, like fire ants, possess a highly potent sting that is able to drive off any animal intruder.

In the US, fire ants and harvester ants (Pogonomyrmex spp.) are notorious for inflicting a painful sting. In order to drive their stingers deep into the wound both ants bite to anchor themselves before plunging their stingers home. A small injection of venom, which causes the burning sensation and allergic reaction, completes the painful sting.

The red imported fire ant, Solenopsis invicta, is a highly invasive species currently distributed across the southern US from coastal North Carolina to east Texas. Local infestations have been found west to California. Possible expansion (based on average annual temperatures) could include all of central California and western Oregon. It is not yet clear how global climate change might affect future distribution of these ants.

These ants can be difficult to distinguish from other small, brown ants, unless you get stung! They make extremely large mound nests that may reach 18" in height and they are very effective predators. In fact, even though this ant is considered to be an invasive pest, when local fire ant populations are eliminated farmers have sometimes noticed a significant increase in other crop pests.

fire ant stings - ARS image

In less than 10 seconds an unwary scientist was stung over 250 times when he carelessly knelt on a collapsed fire ant mound. The sterile pustules developed to this stage in 3 days. Photo by Daniel Wojcik, ARS.

Can fire ants be controlled?

Yes and no. In regions where this invasive species is well established you probably won't be able to achieve permanent control over a large area. However, individual mounds can be eliminated and even entire lawns or pastures can be kept ant-free using the following techniques. Fire ants can generally be controlled with these special baits and insecticides (also see How to Control Fire Ants for additional details).

There is also an interesting biological control option for these invaders. A tiny phorid fly is now being released in experimental attempts at control. The fly develops inside the fire ant and actually decapitates the ant when the adult fly emerges!

Fire ant regulations

In the US and Australia, where the red imported fire ant is known to occur, there are strict quarantine regulations on the export of plant material and mandatory reporting requirements. Contact your local regulatory agency for further information.

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