Botfly

Lore & Background

Botflies deposit eggs on a host or use an intermediate vector such as the common housefly, mosquitoes, or a species of tick. After mating, the female botfly captures the phoretic insect, attaching 15 to 30 eggs onto its abdomen. Larvae from these eggs, stimulated by the warmth of a large mammal host, drop onto its skin and burrow underneath. Some forms of botfly also occur in the digestive tract after ingestion by licking. Mature larvae drop from the host and complete the pupal stage in the soil; they do not kill the host animal, thus they are true parasites. The equine botflies lay eggs on the insides of horses' front legs, which must be carefully removed during late summer and early fall to prevent infestation. In cattle, lesions caused by these flies can become infected by Mannheimia granulomatis, a bacterium that causes lechiguana, characterized by rapid-growing, hard lumps beneath the skin. Without antibiotics, an affected animal will die within 3–11 months. Cuterebra fontinella, the mouse botfly, parasitizes small mammals all around North America.

Reader's Guide

Their life cycles vary greatly, but all larvae are internal parasites, causing myiasis in hosts. The human botfly, Dermatobia hominis, is the only species that routinely parasitizes humans, though other flies episodically cause human myiasis. Botflies use intermediate vectors like houseflies and mosquitoes to reach hosts, and their eggs must be carefully managed in livestock to prevent infestation. In horses, eggs are removed with a sharp knife or rough sandpaper, and dewormers such as dichlorvos, ivermectin, and trichlorfon control infestations. In cattle, bacterial infection from botfly lesions can be fatal without antibiotics. Historically, in cold climates, Hypoderma tarandi maggots were consumed by human populations during caribou butchery, and Pleistocene art confirms their consumption in premodern times. The Babylonian Talmud discusses whether the warble fly is kosher. Botflies are a key example of true parasitism, as they do not kill their hosts.

Did You Know?

• The human botfly, Dermatobia hominis, is the only species of botfly known to parasitize humans routinely.
• Botfly eggs are sometimes deposited on an intermediate vector such as a housefly, mosquito, or tick.
• Equine botfly eggs must be removed from horses' legs with a sharp knife or rough sandpaper to prevent infestation.
• In cold climates, Hypoderma tarandi maggots from caribou were historically consumed by humans.