A member of one of about 60 species of flies in the family Oestridae, in which the larvae are internal parasites of mammals. Some lay eggs directly on the skin of a host, others attach eggs to a smaller insect, commonly a housefly, tick, or mosquito, the eggs hatching when the vector alights on a mammal. The larvae then burrow into the skin, where they feed until mature, then drop to the ground to pupate.