All About Fire Ant Allergy

Allergies to Fire Ant Stings and Bites

The Red Imported Fire Ant. Kansas Dept of Agriculture

What are Fire Ants?

The imported fire ant (IFA) is a type of stinging ant that was accidentally imported into the United States from South America in the early 1900s. Since their introduction into the port of Mobile, Alabama, IFAs have spread into much of the southeastern United States and Texas. IFAs also colonize limited areas of Arizona and California. While there are native species of fire ants present in the United States, they do not pose the same threat to humans as the IFA.

Since IFAs are so common is the southeastern United States, people are frequently stung by them. The chance of being stung is greater than 50% over the course of a year for the general population; the rate is probably much higher for those with outdoor hobbies and occupations, such as outdoor sports and gardening. IFAs have also been reported to sting people indoors, including in nursing homes, private homes and hotels.

When fire ants encounter humans, they tend to sting. People are usually stung multiple times and by multiple ants. An IFA actually grasps a person’s skin with its jaw and tucks its hind end under in order to sting. The ant will then remove its stinger, rotate in a circular fashion, and sting again.

Fire ants are small and typically red or black in color. They live in large colonies in the ground and typically build mounds. Fire ants are related to the flying stinging insects, such as honeybees, wasps, and hornets.

What is Fire Ant Allergy?

Reactions to fire ant stings are very common. There are multiple types of reactions that can occur:

Usual Reactions These reactions occur in essentially 100% of people stung by IFAs and include localized pain, swelling and redness at the site of the sting. Within 24 hours, a pus-filled blister will develop at the site of the sting.

This blister is not infected; it is caused by a component of the fire ant venom.

Large Local Reactions These reactions are probably allergic in nature and occur in up to 50% of people who are stung by an IFA. Symptoms include a large area of swelling, redness, pain and itching at the site of the sting and occur within 12 to 24 hours of being stung.

Anaphylaxis A whole-body allergic reaction, also known as anaphylaxis, can occur in about 1% of people who are stung by IFAs. This reaction can be severe and even life threatening. Symptoms of anaphylaxis from IFA stings may include any of the following:

  • itching all over
  • hives or swelling that spreads from the site of the sting
  • flushing
  • runny nose, sneezing or post-nasal drip
  • itchy/watery eyes
  • swelling of the lips, tongue or throat
  • shortness of breath, wheezing or coughing
  • stomach cramping, nausea, vomiting or diarrhea
  • lightheadedness, fast heart rate, low blood pressure or passing out
  • sense of panic
  • metallic taste in the mouth

Toxic These types of reactions can mimic anaphylaxis, but are due to a very large number of stings -- typically in the hundreds. However, there is no allergic antibody present; symptoms are caused by the large amount of venom that is injected.

How is Fire Ant Allergy Diagnosed?

Typically, the diagnosis of allergy to IFAs is made with a history of an allergic reaction to a fire ant sting, along with a positive allergy test. Skin testing using IFA extract is the preferred method of allergy testing; blood tests, such as a RAST, are reasonable alternatives to skin testing.

The diagnosis of allergy to fire ants should only be performed in those people who should be considered for allergy shots, or immunotherapy, using IFA extract.

Testing is not needed: If a person has never been stung by IFA or never had any symptoms (other than usual reactions) as a result of a sting, there is no need to perform any venom allergy testing.

If a child under 16 years of age only experiences skin symptoms (such as hives and swelling) after a sting, there's no need for allergy testing. This is because anaphylaxis will only occur in up to 10% of future insect stings. However, if there is significant concern about the small chance of anaphylaxis with future stings in this group, testing and treatment for IFA allergy is reasonable.

If a child or adult has a large local reaction where swelling occurs at the site of the sting only, is not usually a reason to perform venom testing or to administer IFA allergy shots. This is because the chance of developing anaphylaxis with future stings is only about 5 to 10% for both children and adults. (A few studies show that these reactions can be decreased with the use of IFA immunotherapy, and this may be required in situations where stings are frequent and the swelling disrupts a person’s quality of life or ability to work.)

Testing is needed: If a person of any age has symptoms of anaphylaxis after being stung. That's because the person has about a 50 to 60% chance that future insect stings will cause a similar reaction. The chance of a reaction to a future sting will decrease over time, but it still remains at about 20% many years after the last sting. Adults (those older than 16 years) with whole-body skin symptoms (hives, swelling) after IFA stings should be tested and treated for IFA allergy.

How is Fire Ant Allergy Treated?

Avoidance The best way to prevent an allergic reaction is to avoid being stung. Here are a few tips:

  • Hire a trained exterminator to treat any known IFA mounds in the immediate area; periodic surveillance for further infestation should be performed.
  • Fire ant bait, obtained at most hardware stores, can be sprinkled onto mounds or over large areas to prevent new infestations.
  • Always wear shoes when walking outside, particularly on grass.
  • Wear pants, long-sleeved shirts, gloves, close-toed shoes and socks when working outdoors.

Treatment of Acute Reactions

Pustules -- There is no known treatment to prevent the formation of pus-filled blisters (pustules). Once a pustule has formed, it should simply be kept clean and dry, and gently washed with soap and water. The pustule is not infected, but secondary infections from disrupting the pustule are very common. Pustules from IFA stings will heal within three to 10 days.

Large local reactions -- These can be treated with over-the-counter anti-inflammatory medications, such as Motrin (ibuprofen), as well as antihistamines, such as Claritin (loratadine) or Benadryl (diphenhydramine). Ice can be applied to the area, and the area can be elevated to decrease swelling. Lastly, a topical steroid, such as hydrocortisone 1% cream, can be applied to the local reaction site.

Anaphylaxis -- The treatment of anaphylaxis from IFA stings is essentially the same as treatment of whole-body reactions to flying stinging insects. This includes the use of injectable epinephrine.

Curative Therapy

Allergy shots, or immunotherapy, using IFA extract can cure fire ant allergy. This concept is essentially the same as shots for flying stinging insect allergy.

Many of the same principles apply.

All people with a history of allergic reactions to insect stings, including children with skin-only reactions and even those with large local reactions, should consider wearing a Medic-Alert bracelet that identifies their medical condition, as well as having an injectable form of epinephrine available for immediate use.


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deShazo RD, et al. Fire ant attacks on residents in health care facilities: a report of two cases. Ann Intern Med. 1999 Sep 21;131(6):424-9.

Reichmuth DA. Monograph on Insect Allergy. 2003. Pp 133-152.

Freeman TM. Imported Fire Ant Allergy. Lecture given at 2004 AAAAI Annual Meeting, San Francisco, CA.

Moffitt JE et al. Stinging insect hypersensitivity: a practice parameter update. JACI. 2004;114:869-886.

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