5 Parasites that Breed On and In Your Skin

The Screwworm
The screwworm larvae can burrow into wounds on animals and humans alike.
The screwworm larvae can burrow into wounds on animals and humans alike.
John Kucharski/USDA

The Cochliomyia hominivorax -- or screwworm -- is a troublesome parasite. The adult form of the insect is a fly that looks similar to a common housefly. The adult female fly seeks out hosts that have open wounds. The fly will lay hundreds of eggs along the edge of the wound. After several hours, the eggs hatch and larvae emerge.

The larvae have a series of ridges along their bodies, which is where the screwworm gets its name. The larvae burrow into the flesh through the wound. There, they feast upon the flesh of the host for several days before emerging to fall to the ground. Then the larvae will burrow into the ground and pupate. It can take between a week and two months for the insects to reach adulthood.

Through careful control efforts, the USDA has all but eradicated the screwworm in North America. The eradication program was simple, but effective -- knowing these flies only mate once, the USDA used radiation to sterilize male flies before releasing them to the wild. The sterile males would mate with females. As a result, the female flies would only lay unsterilized eggs. Within a few generations, the flies were eradicated. Now only incoming animals or humans already infected with the screwworm contribute to any infestation.

You can still encounter screwworms in other parts of the world such as Central America and the Caribbean.

That wraps up our list of parasites that use the skin to breed. To learn more, follow the links on the next page.

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