Screw-worm fly research. Screw-worm fly (Cochliomyia hominivorax) that has been coloured with fluorescent powder at a breeding program used to study and help control this parasitic insect. The fly is coloured to help researchers record its flying distance and habits before being captured again for analysis. Adult screw-worm flies lay their eggs in the open wounds of warm-blooded animals, including humans. The larvae (maggots) then use their sharp mandibles to dig into and eat away the living tissue. This can severely damage or even kill the host. After 3-7 days, the larvae fall to the ground to pupate. Photographed in the factory of the Mexico-American Commission for the Eradication of Gusano Barrenador (screw worm fly), Tuxtla-Gutierrez, Mexico.