Fear the fire ant. Should you step on or near its nest, these insects will quickly swarm onto your feet and legs, biting and stinging repeatedly in an act of vengeance.

Their bites and stings are itchy and painful, too – and for people with fire ant venom allergy, they can lead to a life-threatening allergic reaction, or anaphylaxis.

Where are they found?

Fire ants have been in the United States for more than 100 years, spreading widely across southern and western states, thanks to high reproductive rates.

They often nest in sunny, sandy areas, at the edges of riverbanks and ponds, and in moist areas such as irrigated lawns. They’ve been spotted on beaches as far north as the southern tip of New Jersey, but they don’t typically nest in areas with cold winters.

How do I identify fire ants?

Fire ants are black and red or reddish-brown in color and 1/8 to 1/4 inch in length. But the best way to identify them is by their nests – large, dome-shaped mounds of crumbly earth up to 18 inches across and 8-12 inches high. The nests do not have visible openings unlike smaller anthills.

A fire ant colony can spread across 100 yards and include several queens and 300-500,000 worker ants. Always wear shoes and long pants when in areas where fire ants live.

What should I do if stung?

In most people, a fire ant sting results in an itchy red rash or lump at the sting site within 30-60 minutes. A few hours later, a small blister appears that fills up with pus-like liquid. The blister has little chance of getting infected unless it is opened. Topical ointments and oral antihistamines may relieve the itching.

For people with fire ant venom allergy, symptoms of a sting can include hives, itching, swelling at the sting area and nausea. Anaphylaxis symptoms can include swelling in the mouth or throat, difficulty breathing, vomiting, dizziness and loss of consciousness – administer epinephrine as soon as possible and call 911.

People with known fire ant venom allergy should carry two epinephrine auto-injectors, especially in places where fire ants are common.

Is there fire ant immunotherapy?

Yes – monthly allergy shots help build tolerance to fire ant venom and are safe and effective, says Shayne Stokes, MD, chief of allergy and immunology at Luke Air Force Base in Arizona.

Immunotherapy involves giving gradually increasing doses of fire ant extract to decrease the patient’s sensitivity to the fire ant sting. This can reduce the risk and severity of future allergic reactions.

Reviewed by Bradley Chipps, MD