Bots, the larvae of a species of gadfly, gastero-philus equi. The females deposit their eggs on the sides and legs of horses, where a glutinous fluid attaches the eggs to the hair. The horse in licking himself breaks the eggs, and a small worm adheres to the tongue, and is conveyed with the food into the stomach. There it clings firmly to the cuticular portion of the stomach by means of a hook on either side of its mouth, feeding on the mucus during the winter, and passing out with the chyme at the end of spring, by which time it has attained a considerable size. The larva buries itself in the ground, becomes a chrysalis, and in a few weeks is changed into a fly. The bots cannot, while they inhabit the stomach of the horse, give the animal any pain or cause any injury; for he enjoys the most perfect health while the cuticular part of his stomach is filled with them, and their presence is not suspected until they appear at the anus. They cannot be removed by medicine, because they are not in that part of the stomach to which medicine is usually conveyed; and if they were, their mouths are too deeply buried in the mucus for any medicine that can safely be administered to affect them; in due course of time they detach themselves and come away.
When, after death, the coats of the stomach are found to be corroded and perforated, and when bots are found either in the perforations or already passed through them, other causes have destroyed the stomach. Horses are frequently injured, however, by the medicines which are ignorantly -given to remove the bots. This will easily be understood, when it is stated that bots have lived for many days together in olive oil, and even in oil on turpentine, and that tobacco and nitrous and sulphuric acids do not immediately kill them.