Eggs are deposited in animal skin directly, or the larvae drop from the egg: the body heat of the animal induces hatching upon contact. Some forms of botfly also reside in the digestive tract when consumed by a licking action.
Myiasis can be caused by larvae burrowing into the skin (or tissue lining) of the host animal. Mature larvae drop from the host and complete the pupal stage in soil. They do not kill the host animal, and thus are true parasites (though some species of rodent-infesting botflies do consume the host's testes/ovaries).
The equine bot fly presents annual difficulties to equestrian caretakers, as it lays eggs on the insides of horse's front legs, on the cannon bone and knees, and sometimes on the throat or nose, depending on what type of bot fly does the laying. These eggs, which look like small, yellow drops of paint, must be carefully removed during the laying season (late summer and early fall) to prevent infestation in the horse. When a horse rubs its nose on its legs, the eggs are transferred to the mouth, and from there to the intestines, where the larvae grow and attach themselves to the stomach's lining or they pass into the small intestine and attach there. The attachment of the larvae to the tissue produces a mild irritation which results in erosions and ulcerations at this site.[3] Removal of the eggs (which adhere to the host's hair) is difficult, since the bone and tendons are directly under the skin on the cannon bones: eggs must be removed with a sharp knife (often a razor blade) or rough sand paper, and caught before they reach the ground. The larvae remain attached and develop for 10–12 months before they are passed out of the body with the horse’s manure. Occasionally horse owners will report seeing the bot fly larvae in their horse’s manure. These larvae are cylindrical in shape and are reddish orange in color. In 1–2 months adult bot flies will emerge from the developing larvae and the cycle will repeat[3]. Bots can be controlled with several types of dewormers, including dichlorvos, ivermectin and trichlorfon.