Sunday, September 21, 2014

Bot Flies in Maine

Note: This program first aired on September 20, 2014.

There are so many reasons I am grateful to live in Maine. One of those reasons is the list of things I just don’t need to worry about, like poisonous snakes. The historic and even then very rare reports of timber rattlers in the far western mountains never cross my mind when I am in the woods. Also on that list are poisonous spiders, both poisonous species that are occasionally found here are not native. Brown Recluses and Black Widow spiders make their way into Maine using the time honored tradition of non native species everywhere, they let us transport them, in this case on things like bunches of bananas or grapes, or shipments of used furniture. Our biting insects, though fierce, are typically not deadly. I don’t have to worry about getting malaria or dengue fever from a mosquito bite. Our long winters keep all kinds of tropical maladies and pests from becoming issues here in Maine.

Typically the host survives the bot fly. Not this time.
All of this got turned on its head after a conversation I had last week with Susan Hayward, naturalist extrordinaire and a founding co-director of the Maine Master Naturalist Program. She was commenting on my recent program about horn worms (aka hawk moth larvae) and the curse of the naturalist to be simultaneously fascinated and repulsed by something. She shared her own experience of recently watching a bot fly larva emerge from a meadow vole. Wait, what?? A bot fly larva? We have bot flies in Maine?

Bot flies are a pest that I typically associate with warmer places. The fly lays an egg that ends up contacting your skin, and the egg hatches stimulated by the heat of your body. The tiny larva then burrows below your skin, into your body and sets up shop. It feeds on your flesh and breaths through a hole it maintains at the surface of your skin.  It gets big. Once it is developed enough, it crawls out of your body, drops to the ground and pupates in the soil. Everything about this is simultaneously fascinating and revolting, but it was never something I thought I had to worry about here in Maine.

And it turns out, actually, I was right. We do indeed have bot flies in Maine, but there are lots of different kinds of bot flies, and as parasites, they tend to have good fidelity to their host species. The bot fly Susan saw was in the genus Cuterebra which tend to attack rodents. The flies lay eggs in the entrances to rodent burrows, and as the animal moves past, the eggs hatch and the larvae, well, you know what they do. Apparently, from the number of veterinary web sites out there, its not unheard of for pets to get a bot fly, perhaps from sniffing around rodent burrows. Horse and other live stock owners know about bot flies (other species) too. Apparently I was the only one who didn’t know. And if I had thought about it, all the books I’ve read about the arctic talk about caribou infested with warble flies, which is another name for bot fly, so they venture even further north than here.

It is apparently quite rare but not unheard of for humans to get parasitized by bot fly larvae in this part of the world, but if you need something to worry about, feel free. I am going to put the rodent parasitizing bot flies in the same box in my brain as timber rattlers and brown recluse spiders, the one labeled “cool, possible, but not worth worrying about”. I encourage you to do the same. And one more thing, if you want to know more about bot flies, my advice is, don’t google this while you are eating.

Photos courtesy of Susan Hayward.


Images of Rodent and Rabbit adult bot flies