Screw-worms. Close-up of screw-worm fly (Cochliomyia hominivorax) larvae. These maggots use their sharp mandibles (black) to dig into and eat away the living tissue of warm-blooded animals, including humans. The adult flies lay their eggs in open wounds, and the larvae burrow their way into the tissue. This can severely damage or even kill the host. After 3-7 days, the larvae fall to the ground to pupate.