Ask an Entomologist: Bot Flies

A story in the news today: Man surprised by bot flies on his head! I was looking at some of the comments on that article and others, and thought some general info about bot flies might be useful.

How do you get a bot fly in your head? (Or, Just how freaked out about this should I be??)

This is a true story, and bot flies that attack other mammals are common around the world. Bot flies that will infest humans, however, are rare. Notice that nearly all bot fly stories have one thing in common–a visit to forested areas of Central or South America. If you aren’t there, or visiting there, don’t worry!botfly

The “human” bot fly is really a primate bot fly–it normally infests monkeys. The primate bot fly belongs to the Genus Dermatobia, in the fly Family Oestridae. This family of flies are also known as warble flies, and infest all manner of mammals, including horses, cats, and mice. (One group, called “snot bots”, specializes in living in the nasal passages of hoofed mammals. Ew.)

The primate bot fly is a big fly that looks like a bumble bee–not the sort of thing you’d let fly up and lay eggs on you. How do the maggots get in you, then?
The female bot fly sneakily grabs a mosquito and glues 10 or more bot fly eggs onto her. When the mosquito lands on you for a drink, the warmth of your body stimulates the eggs to hatch and the larva to drop down onto you. And gosh, there’s a convenient hole from the mosquito pre-drilled for the maggot!

About 5-10 weeks later, the maggot burrows into the ground, pupates, and eventually emerges as an adult bot fly. And yes, that does mean you’d have flies in you, under your skin, for over a month.

Several entomologists I know who were infested saw this as an opportunity to expand their insect collection, and let some of the flies grow until they emerged. None of them reported serious pain, although they definitely said it wasn’t comfortable, especially when they were trying to get some sleep.

I’m going to Central America–how do I avoid bot flies?

Short answer: DEET. You may also wish to invest in repellent clothing (that is, clothing that has been treated with a repellent, not just ugly.)

How do you get rid of bot flies?

It’s best if you have a doctor remove them. There’s a risk of infection if you tear or damage the maggot during removal. There are a few other methods you can do yourself; you can read a scholarly article about myiasis, or infection of humans with maggots, here that will detail some of them. (and have more gross photos!)

[edited 9/9/09 to add: rats! that journal article is gone. Here’s the citation: Boggild AK, Keystone JS, Kain KC. Furuncular myiasis: a simple and rapid method for extraction of intact Dermatobia hominis larvae. Clin Infect Dis. 2002.]

NOT FOR THE SQUEAMISH:

{Image from New England Journal of Medicine. } This post is dedicated to Paul Catts, who I miss immensely.

7 thoughts on “Ask an Entomologist: Bot Flies

  1. This reminds me of an encounter between a member of my staff and a visitor to the museum a few years back. She had a botfly larva in a jar and wanted to know what it was. When the staff member asked her where she had gotten it, she said “out of my fatty tissue. I think there’s another one still in there. Here, let me show you…”

    Needless to say, the staff member did not let her show him. We referred to her a doctor and still remember her as botfly lady.

  2. Wow, very interesting! I could not say why I find botflies to be fascinating, but I’ve often thought that forensic entomology would be something to look into. Isn’t there an online class offered through Michigan State? I wonder what else a person would need in the way of background classes to become a CSI …

  3. You can get similar things in Central Africa too. Tumbu flies lay their eggs in mango peels or wet laundry. I had seven in my back because I didn’t iron my shirt before wearing it. Oops.

  4. OW.

    Cordylobia anthrophaga
    is the species name…apparently they are Calliphorids, so blow flies, not bot flies.
    I’ll have to write a new paranoia inducing post! Thanks for the tip!

  5. interesting…i grew up in florida and not only cut bots out of cattle but had two occasions where i was bitten and got ‘infected’. the bots hurt a lot.

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