Tom Turpin
Professor of
Purdue University







Bot Flies Create Gadabouts

Bot flies are hairy flies about the size of honey bees. Immatures of these flies, called bots, are internal parasites of mammals. There are horse bots, cattle bots, rabbit bots, sheep bots, and even human bots. The name indicates the most common mammal host for each of the flies.

There are three kinds of horse bot flies, the common horse bot fly, the chin fly and the lip bot fly. All bot flies create havoc when they fly around horses. Even though the adult flies cannot bite or sting, horses fight the flies. Apparently the buzzing sound of the flies causes the horses to respond as they do.

The horse bot flies glue their eggs to hairs, then when the animal licks or nibbles the hairs the newly hatched maggots move to the digestive system of the horse. These maggots can cause physical injury to the horse and even, at times, block the digestive system.

Cattle bot flies are also known as cattle grubs. The adult stage of this fly is sometimes called a heel fly because it attaches its eggs to the hairs on the heels of cattle. After the eggs hatch, the young flies burrow into the skin. From there they travel to the neck area of the cow and eventually to the back. When they reach the back of the cow, each makes a hole in the skin of the animal through which it breathes. After the grub matures, it emerges through the hole in the animal's skin and falls to the ground, where it pupates.

Like horses, cattle are bothered by the egg-laying behavior of these flies. Animals being attacked by these flies run wildly with their tails over their heads. Such cattle behavior is known as gadding. There is a fly known as the gad fly that does bite cattle, promoting such behavior in its meal target. A human that tends to run about in an uncontrolled fashion is sometimes called a gadabout!

Sheep bots live in the nasal passages of their hosts. When the sheep bot flies are active sheep shake their heads and run, keeping their noses close to the ground so flies can't lay eggs on their noses. The presence of bots in the sinus passages of sheep results in mucus discharge from the nose and labored breathing.  Eventually the mature maggots are discharged from the nose.

The human bot also lives in the sinus passages of its victim. Most of the information regarding this insect came from a researcher in Panama who allowed the fly to lay eggs on him. He then experienced first-hand what it felt like to have maggots in your head. He reported that it was not a pleasant experience — apparently an unnumbered Excedrin headache! Maybe that is why animals threatened by bot flies behave erratically; their genetic code tells them it's not fun to have bot fly maggots living in their innards!


Writer: Tom Turpin
Editor: Andrea McCann