Bots are pesky creatures, capable of causing irritation and physical damage to horses. They aren’t categorized as being the worst of internal parasites, but they can cause problems externally and internally.

The external aspect is primarily one of irritation to the horse. The botfly is about the size of a honeybee, and its prime purpose in life is to lay eggs on the hairs of equine legs, necks, faces, and other parts of the anatomy. They don’t bite the horse, but they do create an irritating tickling sensation as they land to deposit their eggs.

And although we will talk later about “deworming” as a weapon against these parasites, they are not really worms, such as ascarids and strongyles. Instead they are flies, and like other flies their life cycle involves four distinct stages—egg, larva, pupa, and adult fly.

As is the case with other parasites, bots need a host to carry out their life cycle. They are specialists, in that they only attack horses, mules, and donkeys—perhaps zebras as well—and do not seek to use cattle or other livestock as hosts