Bot Fly
Facts About the Bot Fly
The bot fly is the common name of flies whose larvae mature while living as parasites in mammals' bodies.
The horse bot fly secretes a substance that it uses to stick its eggs to the hair of a donkey, mule or horse. The animal licks the hair or rubs its leg with its nose as a means of scratching an itch, and then the larvae enter the host animal's mouth and later find their way to the stomach. They attach to the lining of the stomach and they feed there until they are ready to pupate. Then they drop to the ground within the feces of the animal. The larvae can cause damage to the host's digestive tract and thereby weaken the animal, and a veterinarian will need to be called to eliminate the bots. Bot eggs on a horse's legs can be readily seen- they are generally yellowish in color, and should be removed with a bot knife before the horse has a chance to lick at them and ingest them.
The sheep bot fly lays its eggs inside the nostrils of the host animal – it doesn't even land on the animal, it deposits them while in motion. Each larva works its way into the cavities of the head, and causes vertigo episodes that are known as blind staggers. The sheep may become irritable and turn down food, and the lack of nourishment can lead to death.
The Old World bot fly attacks camels, deer, donkeys, mules, horses and elephants. There is also a species called the warble fly that preys on cattle and other grazing animals. The larva is called a cattle grub or a cattle maggot, and it penetrates the host's skin as soon as it hatches. It will move through the cattle's flesh, which will cause the cow to become irritable and suffer weight loss. The cow will also generally decrease her milk production. The bot larva will settle under the skin of the cow's back, and produce cysts, which are called warbles.
In Central and South America there is a species of bot fly that preys on humans. This fly attaches its eggs to a mosquito that it captures to attach the eggs to, and then lets go. If the mosquito comes into contact with a human or another warm blooded animal and stings it, the fly eggs will hatch and then the larvae will fasten themselves to the mammal's skin. These larvae then bore themselves into the mammal's muscle tissue, causing myiasis.
There are about 150 species of the bot fly worldwide. Most bot flies don't kill the host animal, although some of the species of rodent bot flies will consume the host's testes or ovaries.