Montana Public Radio

Bug Bytes: The Human Botfly

Jun 12, 2020

You’ve taken a remarkable trip to Central or South America. You saw incredible species of birds and mammals, and of course were “wowed” by the amazing insects you discovered. You return with life-long memories, beautiful photos and some souvenirs. But unfortunately some travelers return with an unexpected stowaway...the human botfly.

Human botflies are large, hairy flies that resemble bumblebees. The adult fly is harmless. It’s their larvae that are the stuff of nightmares. They are parasites of mammals. Most often, their hosts are animals like cattle, dogs, cats, monkeys, and pigs. But for an unfortunate few, humans also serve as a suitable host.

A human botfly larvae.
Credit Glenn Marangelo

Interestingly, female botflies lay their eggs on different species of blood-feeding insects…like mosquitoes, biting flies or ticks. When an egg-carrying bloodsucker begins to feed on a warm-blooded host, the body heat stimulates the eggs to hatch upon contact. The fly larvae drop onto the host’s skin and burrow into the wound left by the insect bite.

If left to fulfill its lifecycle, the larvae will grow inside its host for 5 to 12 weeks. Once they get large enough, people report feeling the larvae moving under their skin.

Thanks to rings of backward projecting spines, they are well anchored into place and difficult to remove. By covering the wound with petroleum jelly, beeswax, or even bacon, the parasite is unable to breathe and will emerge enough to be removed with forceps.

Luckily, botflies aren't known to transmit diseases and most cases don't require surgical removal. But take some advice. On your next trip to a Central or South American country…restrict your souvenirs to something like t-shirts or shot glasses.