Tips and Tricks: Identifying red imported fire ants


November 16, 2012

By Dr. Dina Richman
Product Development Manager, FMC Professional Solutions

There are 360 species of ants in the United States, but only one red imported fire ant (Scolenopsis invicta). Here’s what to look for:

• In lawns, fire ant mounds can be flat or dome-shaped, and are usually just a few inches tall. Mounds look like sand that has been “worked,” but can reach up to 2 ft. high.

• In spring and fall, when weather is temperate, watch out for new mounds after a rainfall. Fire ants like to build their nests when the soil is damp and easy to maneuver.

• Fire ant mounds do not have openings in the center top like other ant mounds. They enter and leave the mound through side and underground tunnels.

• If you can safely examine the ants up close, you’ll see that fire ants are reddish brown to reddish black. They vary in length, unlike other ant species that are uniform in size.

• When you disturb the mounds with a long stick, fire ants explode out of the mound and travel vertically up whatever is disturbing them. This vertical climb is important because most native ants will not crawl up objects — or with such speed.

• Another clue is white objects in the soil of the mound. These objects are the eggs, larvae and pupae (the “brood”) of developing fire ants.

• An unfortunate characteristic of the red imported fire ant is the burning sensation of their sting, coupled with the development of a fluid-filled pustule or blister.

Fire ant thresholds

Many states do not offer guidance on fire ant thresholds, and it is up to each pest management professional (PMP) to decide the thresholds with which they are comfortable, while also adhering to integrated pest management (IPM) principles. Here is an example of a threshold strategy:

• Highly trafficked areas with more than one active mound = broadcast treatment of all turf and mound treatments of active mounds.

• Highly trafficked area with zero active mounds, but a history of fire ant activity = broadcast treatment.

• Highly trafficked area with zero active mounds and no history of fire ants = weekly monitoring.

• Low-traffic areas with more than 15 mounds per acre = mound treatments of active mounds and broadcast treatment of entire turf.

• Low-traffic areas with less than 15 mounds per acre = mound treatments only.

• Buildings with more than one active mound within 10 ft. of building = perimeter treatment.

An important aspect of IPM is careful monitoring. Be sure to:

• Inspect high-traffic areas weekly, and low-traffic areas monthly.

• Inspect after rainfall, because fire ants like to build new nests in moist soil.

• Instruct all maintenance personnel to report any mounds.

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