BOTS are a common parasite that can affect horses. They are the immature form (larvae) of the adult flies named Gasterophilus Intestinalis, which look similar to small bumble bees.

The adult flies are not parasitic and cannot feed. They only exist long enough to mate and lay eggs on the horse’s forelimbs and shoulders, in late summer and autumn. Sometimes the eggs can be seen on the abdomen and other areas of the horse’s upper body.