Understanding Bot flies

Bot flies are a common nuisance for horses, and their larvae can create digestive problems if left unmanaged. These flies are most active in late summer and early fall, and their eggs are typically deposited on the horse’s legs, chest and muzzle.

How Bot Flies Affect Horses

Adult bot flies themselves do not bite, but they irritate horses by hovering and laying eggs on their coat. When a horse grooms or licks these areas, the eggs are ingested, and the larvae migrate into the horse’s mouth and eventually attach to the stomach lining.

Why This Matters for Horse Health

While some horses tolerate bots without obvious symptoms, they can sometimes contribute to gastric irritation, ulcers and digestive discomfort. In fact, during gastroscopic exams for ulcers, we often find bots firmly attached to the stomach lining. 

Signs that a horse may have bots include scratching or licking at the legs, chest, or muzzle, irritation from flies during late summer, and in some cases, mild colic or digestive discomfort.