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Pest Problems After Storms – Fire Ants

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Red Imported Fire Ant mound in a field

Fire ant mound in a field

Red imported fire ant us found in 75 of North Carolina’s 100 counties. The  mounds vary in size and shape, usually in direct proportion to the size of the colony and on the type of soil (e.g., sandy soils versus clay). For example, a mound that is 2 feet in diameter and 18 inches high may contain about 100,000 workers, several hundred winged adults, and one queen. Mounds are usually located in exposed areas (rarely in shaded or wooded areas) as shown here. You may accidentally step on a nest or grab fire ants during cleanup activities in the yard.

During floods, fire ants form a raft to transport brood and the queen.

Fire ant “raft” floating on the water surface. (Photo – B. Drees, Texas A&M)

In areas of severe flooding, fire ants will abandon their nests and form  “rafts” which drift in the water until they find ‘high ground’, such as a tree trunk/limb or some other object. In these situations, the ants can pose problems during rescue and recovery efforts and other activities in flooded areas because “high ground” can also be the sides of a boat or the foundation of house..

When disturbed, fire ants will both bite and deliver painful stings. Within 24 hours after a person is stung, a pustule-like sore usually forms at the site of each sting and then usually begins to itch intensively. Scratching the pustule may rupture the skin, potentially leading to secondary infection (particularly if you are working in contaminated waters) as well as scarring. Just as with bee and wasp stings, some people people are highly allergic to fire ant stings and require medical attention after a stinging incident.

Fire ants are particularly fond of greasy-oily foods. While they typically an outdoor problem, disturbances during/after severe weather may bring them indoors in search of food or “high ground” which makes encounters with them more likely.

Here are some suggestions to follow if fire ants are common in your area:

  • Watch where you step when clearing debris in yards,
  • Insect repellents are not likely to be effective against fire ants.
  • When eating outside, keep all food and drinks covered while they are not being consumed. Dispose of food scraps (and disposable dishes, dinnerware, etc.) in garbage bags and trash cans. Keep trashcans covered and (preferably) away from the house (to avoid drawing more foraging ants to where you are working)..
  • Indoors – do not leave food exposed on tables, counter tops, or floors (in the case of pet foods).
  • If your need to treat a fire ant mound that is disrupting cleanup and other activities, drench the mound with a liquid insecticide. Products containing Sevin, cyfluthrin or bifenthrin, lamda-cyhalothrin, and permethrin should work. Be careful when applying pesticides near standing water, ponds and pools. Many of these products have restrictions on how close they can be applied to a body of water. Fire ant baits work well, but they also take significantly longer time to effectively reduce the ant population and may not be as effective when there are other food sources (e.g, trash cans with old food) readily available.. Also, if you have fire ant bait that was damaged by rain or flooding, it’s likely contaminated and won’t be attractive to the ants. A list of products that can be used against fire ants is available in the North Carolina Agricultural Chemicals Manual.

For additional information, consult Control of the Red Imported Fire Ant