Fire ants deliver a simultaneous bite and sting that are very painful and give them their infamous name. The threat of fire ants to healthy, ambulatory adult animals is fairly minimal. However, fire ants can be a significant threat to recumbent (down) animals and to newborns if they lie down or are born on or near an ant bed. Before any field procedure, an essential routine for veterinarians is surveying the planned work area for any fire ant beds.

Immediate clinical signs of fire ant bites include intense pain, pruritis (itching), and erythema (redness of the skin produced by congestion of the capillaries). Fire ant venom is composed mainly of piperidine alkaloids and is less than 1% proteinaceous. Stings usually develop into pustules within 12 to 24 hours due to local necrosis caused by the piperidine alkaloids. Sometimes only secondary lesions such as erythema and epidermal collarettes may be noticed; affected skin may feel thickened and corrugated.

Neonates can be killed if attacked by the many ants inhabiting a mound, but adult animals are unlikely to die as a result of fire ant stings. The overall severity of clinical signs and disease is likely due to the number of ant stings suffered. The author has seen a weanling horse that developed severe laminitis as a complication of multiple fire ant stings with nearly one entire side of the body affected, necessitating euthanasia. Anaphylactoid reactions are rare without massive exposure to stings and occur in those animals hypersensitive to the protein portion of fire ant venom.

Treatment of fire ant stings is largely symptomatic. The ants often remain attached, and mechanical removal or bathing is needed. The main goal of treatment is to reduce pruritis and pain using topical or parenteral corticosteroids (dexamethasone, 0.05-0.2 mg/kg, IV, every 12 to 24 hours) and nonsteroidal anti-inflammatory drugs (flunixin meglumine, 1.1 mg/kg, IV or PO, every 12 to 24 hours). Antihistamines (tripelennamine 1.1 mg/kg, IM, every 6 to 12 hours) may also be of benefit. Affected animals should be observed for any possible secondary complications such as laminitis, respiratory difficulty, abortion, etc. Most will have a full recovery after several days of mild to moderate pruritis and dermatitis.

Contact: Dr. Bryan M. Waldridge, Rood and Riddle Equine Hospital; Lexington, Kentucky.

Map showing distribution of fire ants in the U.S.
Managing Imported Fire Ants in Horse Pastures

Imported fire ants (Solenopsis invicta and Solenopsis richteri) were accidentally introduced into Alabama from South America more than 75 years ago. The Southeastern United States and a few counties in New Mexico and California are infested (see Figure 1) with these insects, which produce painful stings to both people and animals. They live in the soil, with each colony having one or more fire ant queens that lay eggs and control activities within the colony. There can be 40 to more than 300 fire ant mounds per acre in a typical pasture. For an estimate as to how far north imported fire ants can spread, see:  

If fire ants are present in horse pastures, owners need to decide if it is worth treating the pastures. Apart from horse health concerns, these pests can interfere with haying operations and damage electrical equipment. However, fire ants are good predators, and they help reduce tick populations. See for more information about the biology of imported fire ants and their impact.

To reduce the number of imported fire ants in pastures, several baits can be broadcast applied. The bait consists of an active ingredient and a food attractant that has been placed on a carrier particle. The baits are designed to be picked up by foraging fire ants, taken back to the nest, and fed to various members of the colony, including the queen. Depending on the size of the area to be treated, the bait can be applied using a small hand-cranked seeder, a motorized seeder, or an airplane. Cost of a bait application is about $10-$15 per acre. Choose a pesticide that is labeled for pastures or hayfields (versus lawns, turf, and ornamental plants). A variety of baits can be applied to horse pastures, including hydramethylnon, pyriproxyfen, s-methoprene, and fenoxycarb. More information can be found at  

A particular fire ant control product may not be registered (legal to use) in every state. This is especially true for states with very few fire ant-infested counties. Purchase fire ant control material in the state of residence, and ensure the pesticide is labeled for fire ants and pastures. As with all chemicals, follow manufacturer's directions for safe application.

Contact: Dr. Kathy Flanders, Department of Entomology and Plant Pathology, Auburn University, Alabama.

This is an excerpt from Equine Disease Quarterly, funded by underwriters at Lloyd's, London, brokers, and their Kentucky agents.

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About the Author

Equine Disease Quarterly

Equine Disease Quarterly is a quarterly equine disease research newsletter published by the University of Kentucky's Gluck Equine Research Center, and funded by underwriters at Lloyd's of London, brokers, and their agents.

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