Merriam-Webster Collegiate Dictionary - screwworm

 noun  Date: 1879  1. a blowfly (Cochliomyia hominivorax) of the warmer parts of America whose larva develops in sores or wounds or in the nostrils of mammals including humans with serious or sometimes fatal results; especially its larva  2. any of several flies other than the ~ and especially their larvae which parasitize the flesh of mammals