Bot Flys Are Out!

The eggs hatch when the horse licks and rubs them. Once in the mouth, the small bots burrow into the gums and tongue where they remain for about one month and then migrate into the stomach. Upon entering the stomach, the larvae attach themselves to the mucus membrane and remain there for the next eight to 10 months. They detach themselves in the spring and pass through the feces. Once outside the host, the larvae pupate. Mature flies emerge in four to six weeks. The flies mate, the adult females lay eggs, and the cycle begins over again. The flies do not bite, but egg-laying is annoying to the horse. The principal damage caused by the bot is to the stomach lining. In extreme cases, bots can cause a stomach rupture or fatal colic if they block the stomach valve to the small intestine.

Consult your veterinarian for drugs available for internal parasite control. Ivermectin is the de-worming drug of choice be sure to follow the directions on the label before using it. Remove (by clipping or scraping) the yellowish bot eggs from the horse’s hair before they hatch. Then sweep them up and dispose of the clippings and eggs away from feeding areas. Warm water will cause eggs to hatch, allowing small larvae to be killed before they enter the mouth.

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Prepared by Ann Swinker, Horse Extension Specialist