Bot flies don’t bite humans. Adult bot flies have no functional mouthparts and never eat during their short lives. But they do parasitize humans in a way that’s far stranger than a bite: the female bot fly deposits her eggs on a blood-sucking insect like a mosquito, and when that mosquito lands on you, the eggs hatch from your body heat and the larvae burrow into your skin. So while the fly itself never touches you, the result is a living larva growing under your skin for weeks.
How Bot Flies Actually Reach Humans
The human bot fly (Dermatobia hominis) uses a remarkably indirect strategy. The adult female captures a mosquito or other biting insect mid-flight and glues her eggs to its body. When that carrier insect later lands on a person to feed, the warmth of human skin triggers the eggs to hatch. The tiny larvae then drop onto the skin and burrow in, often through the mosquito’s bite wound or a nearby hair follicle. You won’t feel the larvae entering. The initial sensation is no different from an ordinary mosquito bite.
This hitchhiking strategy is why bot fly infestations catch people off guard. You never see the bot fly itself. You just notice, days later, that what seemed like a bug bite isn’t healing.
What a Bot Fly Infestation Feels Like
Once inside, the larva settles into the fatty tissue just beneath the skin and begins to grow. According to the CDC, the result is a raised, painful swelling that resembles a boil or large pimple, often on the scalp, arms, or back. A small central opening remains at the surface so the larva can breathe.
Over the first week or two, you’ll likely notice intermittent sharp, stabbing pains as the larva moves. Many people describe a crawling or twitching sensation. The bump grows steadily, and you may see small amounts of fluid or discharge seeping from the breathing hole. The area around it can become red and tender, but true bacterial infection is relatively uncommon while the larva is alive, because its breathing movements help keep the wound draining.
The larva stays in your skin for 5 to 12 weeks, eventually reaching 18 to 24 millimeters in length. If left alone, it will eventually emerge on its own, drop to the ground, and pupate in soil for about 20 to 30 days before becoming an adult fly. Most people, understandably, prefer not to wait that long.
Where This Happens
Human bot fly infestations are concentrated in Central and South America, ranging from Mexico to Argentina. If you’re a traveler, the highest-risk countries are Belize, Bolivia, and Brazil. A large study of returned travelers found that myiasis (the medical term for fly larva infestation) accounted for 2.7% of all skin-related diagnoses seen in travel clinics, and 80% of those cases were acquired in Latin America. One retrospective study from Israeli travel clinics found that the single most common origin was Bolivia’s Madidi National Park in the Amazon basin.
In sub-Saharan Africa, a different species called the tumbu fly causes similar skin infestations, though through a different mechanism (it lays eggs on damp clothing hung out to dry). In North America, rodent bot flies (Cuterebra species) occasionally infest humans by accident, though this is rare.
How It’s Diagnosed
Most cases are diagnosed simply by looking at the characteristic boil with a central breathing pore. If the larva is close enough to the surface, you can sometimes see its dark posterior end or observe movement. In uncertain cases, ultrasound can confirm a live larva. The imaging shows a distinctive oval mass in the tissue beneath the skin, and when the breathing pore is sealed with ultrasound gel, the larva’s panicked movements create a visible “bubbling” pattern that confirms it’s alive. Doppler ultrasound can even determine the larva’s size and developmental stage.
Removal and Treatment
The standard treatment is physical extraction. A doctor will typically apply local anesthesia, make a small incision if needed, and carefully pull the larva out intact. The key challenge is that bot fly larvae have rows of backward-facing spines on their bodies that anchor them in place, making them resistant to simple squeezing.
You may have seen home remedies online: covering the breathing hole with petroleum jelly, paraffin oil, or even raw meat to suffocate the larva and force it to the surface. These approaches sometimes work, but they’re generally not recommended. A suffocated larva is harder to remove than a living one, precisely because of those abdominal spines. If the larva dies and breaks apart during extraction, leftover fragments can cause infection or a prolonged inflammatory reaction.
After successful removal, the wound typically heals well with basic wound care. Most people recover without complications, though the site may remain tender for a few days and leave a small scar.
Reducing Your Risk While Traveling
Since bot fly larvae reach you through mosquito bites, prevention comes down to the same strategies you’d use against mosquitoes. Insect repellent containing DEET at 25% concentration or higher provides meaningful protection, though studies on biting flies suggest that no repellent offers complete protection. Plant-based repellents containing para-menthane-diol (the active ingredient in lemon eucalyptus oil) have shown effectiveness comparable to or better than lower-concentration DEET products in some studies.
Wearing long sleeves and pants in forested or rural tropical areas helps reduce exposed skin. If you’re spending time in known high-risk areas like the Amazon basin or lowland forests of Belize, tuck pants into socks and treat clothing with permethrin for an added layer of defense. Sleeping under mosquito nets, especially in open-air or rural accommodations, eliminates exposure during the hours when many vector insects are most active.
If you return from a trip to Central or South America and notice a bite that’s growing, painful, or not healing after a week or two, the possibility of a bot fly larva is worth considering. The telltale sign is a visible central pore in the swelling, sometimes with intermittent sharp pain or a sensation of movement beneath the skin.