Tom Turpin
Professor of
Purdue University







Bots in the World of Insects Are Flies

Mention the word "bot" and what comes to mind? Maybe a robot that aids in the manufacturing process. Possibly a computer program on a network that can interact with a computer system or users. Or a mechanized machine controlled remotely by humans. All are known as bots. But long before these modern bots came into existence, a group of insects was carrying the name bot.

Insect bots are flies. These flies get their name from their immature forms known as bots, warbles or grubs. Bot flies resemble bees in size, coloration and hair covering. Bee mimics are common in the insect world. Bees are generally recognized as stinging insects and, as such, are accorded due respect by most other animals. Bot flies gain protection because they look like bees. This resemblance means that most people would not recognize a bot fly if they saw one.

Bot flies are not common insects. So seeing a bot fly is a rare occurrence, even for an entomologist. Recently, as we were getting ready for a noontime jog, a colleague of mine pointed out that a flying insect had just crashed into a wall and landed six legs up on the floor. At first glance, I thought it was a carpenter bee. Then I looked closely at the stunned insect. It only had two wings. Not a bee, but a fly. That floored insect was a bot fly!

Bot fly larvae are internal parasites of animals. That means the larvae live and feed inside of the host animal. The sheep bot fly is an example. This insect is viviparous, a scientific term for an insect that does not lay eggs but deposits larvae instead. Here's how the process works. The sheep bot fly deposits larvae on the nostrils of a sheep. The larvae migrate into the frontal sinuses of the animal. The larvae feed in the sinuses until mature and then are expelled from the nostrils of the sheep. Once expelled, the larvae crawl into the soil where they change into pupae.

Another bot fly is the cattle bot. These flies, as you might have guessed, attack cattle. They also attack deer. The cattle bot is also known as a heel fly because it attaches eggs to hairs on the heels of the host animal. The fly buzzing about the legs causes the animal to kick up its heels and run in an uncontrolled fashion, seeking water or shade. Such behavior is called gadding.

Once the egg of the cattle bot hatches, the young larvae chew through the skin of the host. The larvae, also called grubs, then migrate from the legs to the throat area and then to the back of the animal. Once the larva arrives at the back of the host animal, it chews a hole through the skin. That hole provides air for the larva as it completes development. When mature the grub works its way through the skin and falls to the ground, where it pupates to the adult stage.

Bot flies, as we have seen, attack cattle and sheep. Some also attack horses and are a major pest to these animals. There are bots that are found in rabbits and rodents. Bot fly larvae have also been found in dogs, cats and monkeys.

Even humans are attacked by bot flies. One species of bot fly is even called the human bot fly, although it parasitizes a wide range of hosts, including hogs, cattle, cats, dogs, horses, goats and birds. The human bot has an unusual life history. This bot does not lay eggs directly on a host. It captures a blood-sucking insect, such as a stable fly or a mosquito, and attaches the eggs to that insect. When the blood-sucking insect, known as a carrier, is taking a meal, the bot fly egg hatches and the larva penetrates the skin.

Depositing an egg on a host can be dangerous to the bot fly. So the human bot fly has enlisted the aid of another insect to deliver bot fly eggs to a suitable host. Who says there is no such thing as an intelligent bot?


Writer: Tom Turpin
Editor: Olivia Maddox