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Fire Ants: The Invasion Continues

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Originally Published April 1, 2005

The number of fire ants seems to have increased noticeably in central Oklahoma in the last couple of years. The number of mounds we can see and the numbers of calls and complaints the Noble Research Institute receives have skyrocketed.

Fire ants (red imported fire ant, if you prefer the full name) are native to South America. They are thought to have first entered the United States on a cargo ship in Mobile, Alabama, in the 1930s. They rapidly spread throughout the southeastern United States and are now thought to infest more than 320 million acres in 13 states.

Fire Ants or Red Harvester Ants

Not all ants are fire ants. Fire ants make a loose mound that looks somewhat like a gopher mound and does not have a single large entrance. If you disturb a fire ant mound, the ants (which are relatively small and reddish brown) seem to boil out of the mound. From personal experience, they are extremely aggressive and can sting multiple times (usually seven to eight stings per ant). Some people are highly allergic to their stings, but for most of us, it just hurts a lot.

If you have large ants in a low circular mound that has a large entrance hole in the center and vegetation cleared around the edges, these are probably red harvester ants. These can inflict a painful sting, but are much less aggressive than fire ants and are not usually a problem. You might consider keeping these guys around because they will try to keep fire ants at bay since ants are territorial.

Predators of Fire Ants

Fire ants are difficult to get rid of for several reasons. A mound may produce hundreds of queen ants in a year. Of course, most of the new queens do not produce a viable new colony of ants. They can spread by walking to a new area, by flying a considerable distance to a new area or by forming a raft and floating to a new location. They are very aggressive and eliminate many of their predators.

There are some biological predators of fire ants. Armadillos eat a few ants. Maybe this makes you feel a little better about having your yard and pasture dug up. There is a tiny predator insect of fire ants called the phorid fly which lays an egg in a fire ant's body. The developing larva of the fly destroys the fire ant. About 12 hours later, the ant's head falls off and the phorid fly larva dines inside until it emerges. While the flies are active and looking for victims, the ants will hide from them, with good reason. This disrupts the food supply to the mound and can damage the queen and the mound.

OK, I've got 'em, and I want to get rid of 'em. What can I do?

This depends on where the ants are and what your objectives are. There are three basic methods of control you can use: organic, individual mound chemical treatment or broadcast bait insecticides.

Organic Treatments

There are not many effective organic treatments. Possibly the best one is to pour 2 to 3 gallons of boiling water on the mound. This can be about 60 percent effective if it is done after a rain and the mound has been freshly re-built. It probably goes without saying that it will burn if you spill boiling water on yourself instead of the mound. The boiling water will also kill any surrounding vegetation. Another organic treatment method that has fair success is to apply diatomaceous earth to the mound. Diatomaceous earth can damage your lungs if you inhale it, so be careful. I guess praying for a very cold winter would also be a form of organic control, because the fire ant numbers are decreased by extremely low temperatures.

Individual Mound Insecticides

There are many insecticides that can be used for individual mound treatments. Be sure to check the label to determine the safety for children and pets if the mounds are in your yard. Do not disturb the mounds prior to treatment. Some mound treatments can be used as a dust and not watered in. Some are used as drenches and must be mixed with fairly large volumes of water to work properly. Be sure to consult the label for the proper way to use the insecticide.

Individual mound treatments work well if you have a small number of mounds in a lawn setting. If you have large numbers of mounds in a larger acreage, a broadcast bait insecticide treatment is a better bet.

Broadcast Bait Insecticides

The individual mound treatments are contact insecticides that kill the insects very quickly. The broadcast bait treatments work a different way. The insecticide is applied onto food for the ants. The ant food plus insecticide bait is broadcast applied to the land. The bait is collected by the worker ants and fed to the members of the colony, including the queen. If the queen dies, there will be no more ants produced in the mound and the mound will eventually die.

Baits can also be used as individual mound treatments. If you use them this way, apply them evenly in a 2 to 3 foot radius of the mound. Bait treatments take much longer to see results, but the results are usually longer lasting. If you're the bloodthirsty, revenge-minded type, you'd probably prefer the individual mound treatments with contact insecticides.

Some report that their best results have occurred with the Two-Step Method. Broadcast the bait according to label directions and then individually treat the mounds two or three days later. The fire ants you miss with the individual treatment have a good chance of being killed as they ingest the bait.

Some of the bait treatments have a short grazing restriction following application, and some have no grazing restriction. Be sure to check the label to determine if you need to move the cattle during and after treatment.

For More Help

All experts agree that fire ants will not be eradicated and are here to stay in some form or fashion. However, there are steps you can take to reduce their numbers to a more pleasant level.

If you have questions about fire ant control, call the Ag Helpline at 580-224-6500.