Being pregnant, as it turns out, isn’t the only way to give birth. Humans are often hosts to a variety of creatures that temporarily reside within us – unconsciously, we let them eat, sleep and be born anew.
One of the most interesting forms of this involuntary hosting is myiasis, or the infection of a host with the larval stage of flies. The fly you really need to watch out for, especially when traveling in Latin America, is Dermatobia hominis. Commonly known as the bot fly, this charming member of the fly family Oestridae has a particular fondness for humans as surrogates for its soon-to-be orphaned larvae.
I was chosen to rear some baby flies for the first time in 2010, while doing field research on the tropical biology of monkeys in the Peruvian Amazon. The first indication that this particular raised bump was different from the myriad bites on my body came in the form of a muted, yet stabbing pain. This caused me to examine my arm in some consternation, for a biting insect, but to my chagrin the pain was emanating from within me. I traced it to a slight, reddish bump with a small puncture wound on top that glistened in the light. As I peered thoughtfully at the spot in question, a thin white tube popped out of the wound and retreated in a flash.
I had just met my new baby fly.
Turned off yet? Don’t be. At least, not yet. You haven’t watched one being removed from someone’s head, have you? Then you’re fine.
Here are 20 things you didn’t know about bot flies:
1. Although D. hominis is the most common species to occupy passing humans as hosts, it has quite a taste for a variety of other animals, including poultry and livestock.
2. Flies arrive to their human host by way of a courier, typically a mosquito (although other insects can be chosen as well), which are captured by the adult female fly and slathered with larvae.
3. These chosen insects, with unerring accuracy, zone in on some exposed part of human anatomy for a feed – and unselfishly deposit the larvae near a nice open wound.
4. The larvae, with remarkable perspicacity for their age, sense the warmth of the human body, hatch out of their shells, and burrow under the skin of the host.
5. The tiny puncture they make to, literally, get under your skin is the same hole they use to breathe out of.
6. Bot fly larvae can grow up to at least a centimetre in length, and are rather chubby around the middle.
7. They are covered in a beautiful spiral pattern with spines. Not just any spines, spines that point backward and are designed to make it very uncomfortable for the host (and possibly the larvae themselves) to exit their chosen, well, for want of a better word, restaurant table.
8. They will remain in you for anywhere from 6 to 12 weeks, although it must be a remarkable fly indeed to be able to accomplish in 6 weeks what it takes others 12 to achieve!
9. If left alone, after a fair amount of squirming and as one doctor puts it, lancinating pain (of the cutting or piercing variety), the larva will voluntarily leave you and take up residence in the nearest patch of soil it can find.
10. It remains as a pupa in the soil for 4 to 11 weeks (again the uneven growth trajectories among pupae!) after which it will emerge as an adult, no doubt with a bright future in parasitism ahead of it.
11. YOU CAN REMOVE BOT FLIES FROM YOUR PERSON BEFORE THEY GET BIG. Given that this fly parasitizes everything from humans to cattle, from Mexico to Argentina, people have been giving its removal a fair amount of thought.
12. If you attempt to encourage it to leave before it is ready, it will not go quietly. Damaging the larva in any way typically leaves you with one dead maggot in you, with backward facing spines making it all the more difficult to remove. DO IT ANYWAY.
13. The suffocation-by-tape method: Cover the nesting place with a piece of duct tape. Grit teeth while larva squirms. Wait for it to die. Extract in about 24 hours. Unfortunately, the respiratory tube often comes off with the tape, and then minor surgery is required to get the larva out. Leaving it in isn’t an option either, since infections ensue with worse outcomes.
14. The bacon-is-for-bot-flies method: Tape a piece of bacon over the wound. Bot fly smells bacon. Bot fly prefers bacon to you, and opts for a better mother. Exit bacon and fly. Some times, you just have no bacon. Or your bot fly has poor taste and opts for you instead.
15. Nail polish to the rescue (my personal favourite): Cover the wound with a layer of clear nail polish. Let dry. Add more layers. Bot fly begins to suffocate and exits the nest to rest sweetly under the nail polish for subsequent removal.
16. The venom extractor, which apparently is bloody awful at doing what it is meant to do, is now touted as THE tool to remove stubborn or dead bot flies from their human hosts. No joke. Brief report in the Journal of Clinical Infectious Diseases titled “Furuncular myasis: A simple and rapid method for extraction of intact Dermatobia hominis larve” was published in 2002 and the authors are absolutely batty about venom extractors.
17. If this article is a little too late for you, and you accidentally let the bot fly grow in you, I truly am sorry, because the removal hurts like hell and attracts a lot of onlookers.
18. The adult fly that is born looks like this: (however, there’s no point running when you see one because it’s the mosquitoes that will eventually get you)
19. Bot fly parasitism has been suggested as a primary correlate for mortality among some howler monkey populations. The guilty culprit is aptly named Alouttamyia baeri.
20. Data from over 30,000 white footed mice show that bot fly infections negatively impact reproduction; however, in the absence of successful reproduction, they refocus their energies on body condition, and thus ultimately have increased lifespans!!
Boggild A.K., Keystone J.S. & Kain K.C. (2002). Furuncular Myiasis: A Simple and Rapid Method for Extraction of Intact Larvae, Clinical Infectious Diseases, 35 (3) 336-338. DOI: 10.1086/341493
Burns C.E., Goodwin B.J. & Ostfeld R.S. (2005). A Prescription for a Longer Life? Bot Fly Parasitism of the White-Footed Mouse, Ecology, 86 (3) 753-761. DOI: 10.1890/03-0735
MacNamara A. & Durham S. (1997). Dermatobia hominis in the Accident and Emergency Department: “I’ve got you under my skin”, Emergency Medicine Journal, 14 (3) 179-180. DOI: 10.1136/emj.14.3.179
Milton K. (1996). Effects of Bot Fly (Alouattamyia baeri) Parasitism on a Free-Ranging Howler Monkey (Alouatta palliata) Population in Panama, Journal of Zoology, 239 (1) 39-63. DOI: 10.1111/j.1469-7998.1996.tb05435.x