Warning: This is definitely another one of those “that which has been seen cannot be unseen” kind of articles. View with discretion.
Dermatobia hominis is a species of botfly which parasitizes humans, with a range from Southern Mexico down about halfway through Chile and Argentina. The botflies use 40 different species of mosquitos and other insects as a vector to infect humans. The fly captures the vector, deposits the eggs onto it, and releases it. When the mosquito bites a human to feed, the eggs are dropped onto the skin. Body heat causes the eggs to hatch, and they quickly burrow under the skin through the bite hole provided by the vector.
Over the course of the next 8 weeks, the larvae develop. After they have grown large enough (about 18-24 mm) the larvae exit the skin and drop to the soil where they will pupate for about a week before starting over with the life cycle.
Botfly larvae can develop wherever the eggs wind up, which can sometimes have some pretty horrifying results. In rural Honduras, the Air Force Mobile Ophthalmic Surgical Team extracted a botfly from the eye of a five-year-old male patient. The little boy was put under anesthesia and the larva was extracted from his eyeball.
Images credited to Capt Randall L. Goodman, USAF et al., 2000