You get a botfly infection when a larva of the human botfly (Dermatobia hominis) burrows into your skin, but the twist is that the botfly never lands on you directly. Instead, the adult female botfly captures a mosquito or other blood-feeding insect and glues her eggs to its body. When that mosquito later lands on you to feed, your body heat causes the eggs to hatch within about five minutes, and the tiny larvae drop onto your skin and burrow in.
How Botflies Use Mosquitoes as Delivery Vehicles
Adult female botflies are large, buzzy insects that rarely interact with humans themselves. Their strategy is indirect: they catch a smaller blood-feeding insect, typically a mosquito, and cement anywhere from 10 to 50 eggs onto its abdomen. The mosquito then goes about its normal routine, looking for a blood meal. The moment it lands on a warm-blooded host, the heat triggers the eggs to hatch almost immediately.
The freshly hatched larvae, each barely visible to the naked eye, crawl off the mosquito and penetrate the skin. They can enter through the mosquito bite itself or through a nearby hair follicle or pore. You won’t necessarily feel this happening. The process is painless at first, and most people don’t realize anything is wrong until days later when a bump begins to form.
Where Botflies Are Found
The human botfly is endemic to a band stretching from southern Mexico through Central America and down to northern Argentina. These flies prefer hilly, moist, cool secondary forests, particularly the coffee-growing highlands of countries like Belize, Costa Rica, Panama, Colombia, and Brazil. If you’re hiking, working, or vacationing in tropical or semi-tropical regions of the Americas, you’re in botfly territory.
Botflies also infest cattle, dogs, and other mammals in these regions, so the flies are well-established in rural and agricultural areas. You don’t need to be deep in the jungle to encounter one. Cases regularly occur in people who spent time at eco-lodges, farms, or even well-traveled tourist areas within the endemic zone. Most cases seen by doctors in the United States, Canada, and Europe involve travelers returning from these regions.
What Happens After the Larva Enters Your Skin
Once under the skin, the larva feeds and grows over a period of 6 to 10 weeks. It develops through three stages, eventually reaching roughly one inch in length. Throughout this time, it maintains a small breathing hole at the skin’s surface, which is one of the telltale signs of infection.
What you’ll notice first is a raised, reddish lump that looks like a large pimple or boil. It doesn’t heal. Over time, it grows and may become painful or itchy. Many people report feeling occasional sharp, stabbing sensations or a distinct feeling of movement under the skin, especially at night when the larva is more active. A small amount of clear or bloody fluid may drain from the central pore.
The lump typically appears on areas of exposed skin: arms, legs, scalp, and back are common sites. Unlike some other parasitic infections, the larva stays put. It doesn’t migrate through your body or burrow deeper into tissue. It anchors itself in the fatty layer just beneath the skin and remains there until it’s either removed or completes its development and drops out on its own.
How Botfly Larvae Are Removed
If left alone, the mature larva will eventually exit the skin on its own after about 10 weeks, drop to the ground, and pupate into an adult fly. Most people understandably don’t want to wait that long.
The most reliable removal method is minor surgery. A doctor numbs the area with local anesthetic and makes a small incision to extract the larva intact. This matters because the larva has rows of tiny backward-facing spines that anchor it in place, making it difficult to simply squeeze out. Crushing or partially removing the larva can lead to infection or a strong inflammatory reaction.
A common home remedy involves covering the breathing pore with petroleum jelly, nail polish, or a strip of raw bacon. The idea is to suffocate the larva and force it to wiggle closer to the surface, where it can be grasped with tweezers. This sometimes works for early-stage larvae but carries a risk of incomplete removal. If you suspect a botfly infection, having it professionally extracted is the cleaner option.
How to Prevent Botfly Infection
Since botflies reach you through mosquitoes, preventing mosquito bites is your primary defense. Insect repellents containing DEET are effective, with protection time increasing at higher concentrations up to about 50%, after which additional concentration doesn’t add meaningful benefit. Products with less than 10% active ingredient typically offer only one to two hours of protection. Picaridin, oil of lemon eucalyptus, and IR3535 are also effective alternatives.
Clothing is your second layer of defense. Long sleeves, long pants, boots, and hats all reduce exposed skin. Tucking pants into socks and shirts into waistbands eliminates gaps where mosquitoes can reach bare skin. For additional protection, you can treat clothing and gear with permethrin at a 0.5% concentration, which repels and kills mosquitoes, ticks, and other biting insects. Treated items need 24 to 48 hours to dry before packing.
If you’re staying in rural or forested areas within the endemic zone, sleeping under a mosquito net adds protection during nighttime hours when mosquitoes are most active. Screened or air-conditioned accommodations significantly reduce your exposure as well. These precautions aren’t specific to botflies. They protect against dengue, malaria, Zika, and every other mosquito-borne threat in the tropics, making them worth the effort regardless.