More than you ever wanted to know about the Botfly

Eww, gross. [Link]

Bot flies (Order Diptera, Family Cuterebridae) are large, stout bodied, hairy flies that resemble bumblebees. The botfly egg is deposited by a mosquito or sometimes by another insect. The larva grows in the host's body until it is fairly large. The botfly larva can easily be killed by taking away its air supply -- by putting vaseline or similar on the skin where the lump is, but then you still have to extract the larva. Adult botflies have nonfunctional mouthparts and do not feed. Larvae of this species parasitize wild and domestic rabbits. Females deposit their eggs in or near the entrance of their host's burrow. Bot fly larvae penetrate their host through the skin or natural body openings after hatching. The larvae form a tumor (called a warble) in the subdermal zones of their host and remain at this location until larval development is complete. Larval development varies among species, ranging from 20 to 60 days. Before pupating, the larvae leave the host's skin and drop to the soil.

Lots of testimonials from victims.