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. Lice are normally species-specific external parasites.