JUNE
2010

 

By
Tom Turpin
 
Professor of
Entomology
Purdue University

 

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Check out these books by Tom Turpin:

Flies in the face of fashion

What's Buggin You Now?

 

 

 

06-10-10

Download the audio of On Six Legs: MP3, WMV.

Uncommon Bot Flies Have Recognizable Buzz


A high-pitched buzzing sound, almost a whine, followed by a quick-paced tapping against the windowpane caught my attention as I read the paper the other evening. Home invaders of the insect type are not uncommon during the summer months. But the sound and the behavior indicated that the insect was an infrequently encountered type of fly - a bot fly.

What then ensued was a chase-and-capture scene suitable for a YouTube video. The insect was eventually secured in a device that most people call a butterfly net. I happen to keep a net in the garage for just such occasions! The insect that was trying to escape through the sunroom windows did turn out to be a bot fly.

Bot flies are rather large, hairy flies that resemble bees. The name bot apparently is of German origin from the 16th century and was used to describe the maggots of flies that feed in the bodies of mammals. The adults of those maggots have therefore become known as bot flies.

The bot fly that showed up in my house turned out to be a rodent bot fly. That means that maggots of this type of fly are commonly found living and feeding in the bodies of living rodents, such as mice, rats, squirrels and chipmunks.

While bot fly common names refer to specific animals, such as horse, sheep, reindeer or rodents, the maggots of a particular species are sometimes found in animal hosts other than their namesake. For instance, rodent bots are also found in rabbits, animals that technically are not rodents.

So how does this bot-fly thing work anyway? Well, the bot fly maggots feed inside a living mammal. Some make their home in the nasal passages and sinuses of the host. That is the case with the sheep bot and for that reason the insect is sometimes called the sheep nose bot. The horse bot maggots live attached to the stomach lining of horses. The maggots of cattle bots move throughout the cows body but end up under the skin of the back of the animal where they are known as warbles.

Of course, like in many insects it is the role of the adult bot fly to place the egg on an appropriate host. The cattle bot attaches eggs to hairs on the heels of cattle where the newly hatched maggot chews through the skin to begin its life in the host. Because of this egg-laying behavior the fly of the cattle bot is sometimes called a heel fly.

The horse bot fly also attaches eggs to the leg hair of the animal. When the horse licks its leg, the egg hatches; the maggot gets swallowed and then can attach to the stomach wall. Sheep bot flies actually deposit maggots directly into the nasal passages of sheep. That is why sheep run around and try to keep their noses near the ground when the flies are actively trying to lay eggs.

In all cases, when the maggots have completed their life cycle, they abandon their mammal hosts and fall to the ground, where they pupate into the adult fly stage. In the case of rodent and cattle bots, the maggot uses a hole in the skin of the animal to drop to the ground. Sheep bots, to put it insensitively are "snotted out" through nasal discharge. Horse bots exit the animal in the manure.

If you find all of this a bit disquieting you may want to stop reading. There is a bot fly named Dermatobia hominis that attacks humans. This tropical insect also attacks a lot of animals, including other primates, but it is the only bot fly that dines upon human flesh. This fly is native to Central and South America and sometimes infests visitors to that part of the world. The human bot maggot, like the rodent bot, feeds under the skin and needs to breathe through a hole in the host's skin.

Unlike other bot flies, the human bot does not lay eggs directly on the host. The human bot attaches an egg to a female mosquito or other species of arthropod that seeks human blood meals. When the carrier creature feeds, the bot fly egg hatches, and the maggot penetrates the skin and begins to feed. I guess it's not easy to lay an egg on a human if you look and sound like a bumble bee!

 

 

Writer: Tom Turpin
Editor: Olivia Maddox