Dermatobia hominis – Warble Fly
The Human Bot Fly Causes Painful Lesions in Human Skin
Dermatobia hominis needs a warm-blooded host for its larvae to feed on. Humans are often the unwitting hosts for these large maggots.
The human bot fly, Dermatobia hominis, is one of the warble flies, or skin bot flies, (Family Oestridae)—unpleasant insects that need a living warm-blooded host to complete their larval stage. The large maggots of this species live just underneath the skin, feeding on host tissues and fluids until they are ready to pupate.
The adult female D. hominis is a large warble fly, about 15 to 18 mm long. It has a yellowish face and orange legs, a dark blue-black thorax and a metallic blue abdomen.
Where is Dermatobia hominis found?
The human bot fly is a forest fly, a pest of Central and South America from Mexico south. Though D. hominis infests cattle more often than it does people, and people who live and work near cattle are at higher risk, it’s not uncommon for tourists from North America and other parts of the world to acquire a few warble fly larvae while on vacation.
How do you get human bot fly larvae?
The adult female D. hominis has a curious way of depositing her eggs. Not a bloodsucking insect herself—in fact, she does not feed at all—she captures a bloodsucking insect of a different species and attaches her eggs to the belly of her captive before releasing it. Various bloodsucking species are suitable. Later, when the insect carrying the eggs bites a warm-blooded animal, the eggs hatch and larvae emerge.
With in an hour of hatching, D. hominis larvae penetrate the skin of the host, either through the bite wound, or through intact skin. They don’t travel about once they are inside, but set up a little cavity in which they rest and feed, with a tiny opening to the outside air. The larvae grow larger over a period of up to six weeks.
What does a bot fly lesion look like?
At first, most people are unaware that they have bot fly maggots living under the skin. Because the larvae are near the site of an insect bite, the lesion is usually mistaken for an insect bite at first, and things don’t get more uncomfortable for several weeks or more. The growing maggot, however, eventually causes a swollen painful and itchy lesion that may be mistaken for a boil or infected fly bite. The warble fly maggot grows to about 18-24mm long, and has several bands of hooklets that hold it in place. Near the surface of the skin, its tail end is long and thin, and positioned in the tiny opening that allows it to breath. This opening and the respiratory “spiracles” of the maggot are visible to the careful observer.
People often seek treatment for infection and are given antibiotics, an approach that doesn’t bring relief. Left alone, the mature D. hominis larvae eventually emerges on its own and the lesion heals. However, if the larva is recognized, it can be gently excised with a sharp scalpel blade. Natural remedies include covering the lesion with petroleum jelly or bacon fat to cut off the maggot’s air supply and force it to emerge.
Other insects and arachnids that plague humans:
Other subjects in Fish and Insects:
Sources:
Beaver, Paul Chester, Rodney Clifton Jung, and Eddie Wayne Cupp. Clinical Parasitology 9th ed. Philadelphia: Lea and Febiger, 1984.
Garcia, Lynn S. and David A. Bruckner. Diagnostic Medical Parasitology 3rd ed. Washington: ASM Press, 1997.
Roberts, Larry S. and John Janovy Jr. Foundations of Parasitology 6th Ed. Boston: McGraw Hill, 2000.
