Small But Mighty: The Fire Ant and It’s Venom

Michelle Willis, CVT, RVT
Veterinary Information Specialist 

This post was inspired by an incident that occurred at home with my own dog, Zoey (*names have been changes to protect the victim). Living in the SE of the country, we are no stranger to all sorts of insects. Zoey, who is our very curious Boston Terrier, is a known insect chaser. Previously, her run-ins with the Insecta species have been relatively benign. That was until the other day, when her curiosity led her to stick her lovely smushed face in some fire ants. While the bites occurred while she was out in our fenced yard, the severity and signs seen were somewhat like those that occur when humans are bit my fire ants…those suckers hurt!

I initially found that Zoey was depressed and mopey, which is very abnormal for her. Then I noticed that her lower jaw was very swollen and red. Thankfully her airway was not involved, or we would have been on our way to the emergency clinic. In the days that followed, the area on her chin became increasingly inflamed, and severely itchy. She scratched so much to the point that she was starting to do damage to the skin. Meanwhile, on her groin, there appeared two papules that looked identical to those that humans get after fire ant bites, and the cause of her symptoms was confirmed. Throughout the time, she was treated with pain medication, anti-itch mediation, as well as daily disinfecting of the skin on her chin followed by topical steroids. Once the itching was lessened, the skin began to heal. Now, almost two weeks later, she is starting to return to normal.

All of this got the nerd in me thinking…what exactly is the science behind a fire ant and its bite? Here’s what I found out:

Fire Ants were first imported accidentally (what a big mistake that was!) into Alabama from South America in the 1930’s and have continuously been expanding across the United States, even into Puerto Rico. In humans, fire ant stings usually occur on the feet or legs after accidentally stepping on a fire ant mound. With animals (both companion and wildlife such as deer and rabbits) the eye is the most critical site for fire ant damage. The eyelids may slough along their margins when enough sting sites are present. Fire ants can also sting the corneal surface. We will often see bites on the feet, and nose/muzzle areas.

Confirming my suspicions, during the summer fire ants produce the largest amount of venom and therefore the stings are largest and most painful. Each ant produces very little venom, less than 1 µg. Proteins make up only a small portion of the venom, adding up to just a few nanograms per ant, with the rest consisting of basic compounds called alkaloids.  The specific alkaloid toxin is Piperidine, which is a relative of piperine, the main chemical ingredient in black pepper.

People and animals vary greatly in their sensitivity to fire ant stings. Some claim to be “resistant” to the venom. Others are hypersensitive to it or may have other medical conditions (such as a heart condition or diabetes) that can result in serious medical problems or even death from a single sting. Secondary bacterial infection can also be a problem and might require medical management. While most people and animals can tolerate many stings, severe allergic reactions (anaphylaxis) occur.  For further information on the signs of anaphylaxis, please see the following blog post by my awesome colleague:

So, let’s get rid of the fire ants, then? That can bring to light another (somewhat related toxicity) – Some (not all) Fire Ant killers contain Acephate. Acephate is a moderately toxic Organophosphate. There are some ant killers for fire ant mounds that contain up to 75% acephate as active ingredient.   So, what does that mean for pet safety?

Well, it is best to PREVENT any pet exposures, by blocking of the areas treated and not allowing pets to go outside unsupervised when these products are in use in a yard. However, if pets are able to ingest the Fire Ant Killer (again, likely curious dogs that stick their face in anything), we can see some very concerning signs such as: drooling, discharge from the eyes, uncontrolled urination and defecation, vomiting, diarrhea, tremors, muscle weakness, walking wobbly). Signs are normally seen within 6 hours after ingestion and can be life threatening. However, your veterinarian does carry the antidote! Hooray!

If your pet is exposed to either fire ants or their killer, please contact your veterinarian or Pet Poison Helpline® Immediately.