Egg -- The eggs are yellow or black and are attached singly to the hairs of the horse. They can be easily seen on the hair on the legs and mane.
Larva -- Mature larvae may be up to 20 mm in length with 5 to 8 rings of spines.>\
Pupa -- When mature, the larvae release from the stomach and are passed with the feces. The larvae will burrow beneath the soil surface and pupate. Adult flies will emerge from the pupae in 20 to 70 days.
Host -- Horses are the normal hosts for these bot flies, but dogs, rabbits, crows, and (rarely) men have become infected.
Damge -- The larvae damage the horse by interfering with the passage of food, causing stomach lesions that can become a site of secondary infection and by causing restlessness when the larvae are in the rectum prior to passage. Horses with large numbers of bots become run down and unthrifty.
Life History -- Horse bots will deposit up to 1,000 yellow eggs attached to the hair of the forelegs, belly, flanks, shoulders, and mane. The horse licks the eggs off the hair when grooming and the sudden increase in temperature of the horse's mouth stimulates the eggs to hatch. The larvae then move to the stomach where the second and third stage remain until spring or early summer. At this time they are passed with the horse's droppings and pupate. The nonfeeding adults emerge, mate and begin to lay eggs in early summer. The life cycle takes one year. The nose bot strikes the horse on the nose, laying black eggs on the fine hairs on the lips. The throat bot lays its eggs under the chin of the horse which sometimes causes the horse to throw its head up from the irritation. The life histories of the nose and throat bot flies are similar to that of the horse bot fly.