Once outside, the bot hatches into an adult fly, and the cycle begins again. The bot fly population is most active in the late summer and fall. Bot flies do not feed. Control is directed at egg removal from the hair and a dewormer to kill the bots in the stomach. One month after a killing frost which will kill the remaining eggs on the hair, a boticide dewormer is administered.
Female worms are normally full of eggs which pass out in the feces.
Additional female pinworms crawl out the anal opening and deposit their eggs on the surrounding skin, causing irritation and itching to the host. For relief, the horse usually rubs against a fence post or other solid object, resulting in hair loss near and on the tail and occasionally producing a secondary infection. The mature female has a slate-grey or brownish color and a narrow tail which may be more than three times as long as the rest of the body. The life cycle is completed in five months. Pinworms are actually less damaging to the equine system than any other internal parasite group.