Screwworms

Definition

The larval stage of certain blowflies (family Calliphoridae, genus Cochliomyia) that cause obligatory or facultative myiasis in warm-blooded vertebrates. Primary screwworms, larvae of Cochliomyia hominivorax, feed on living tissue, creating deep, pocket-like wounds; secondary screwworms, larvae of C. macellaria, invade only necrotic tissue. The term distinguishes these New World species from Old World screwworms (Chrysomya bezziana and related taxa).

Etymology

From the screw-like appearance of the larvae when viewed in wound tissue and their habit of burrowing in a spiral pattern.

Example

Cochliomyia hominivorax screwworms infest fresh wounds on cattle, burrowing deeper as they feed and enlarging lesions that can attract secondary infection or additional oviposition; the United States–Mexico eradication program using sterile insect technique eliminated this species north of the Darién Gap.

Synonyms

• screw-worm larvae
• myiasis-causing larvae (in context)

Related Terms

• myiasis
• Cochliomyia
• Calliphoridae
• obligate parasite
• facultative parasite
• sterile insect technique
• Chrysomya
• blowfly
• wound myiasis
• zoonotic disease
• veterinary entomology

Usage Notes

In strict usage, 'screwworm' refers to the larva, not the adult fly; specialists distinguish primary (living-tissue) from secondary (necrotic-tissue) forms. The common name applies specifically to New World Cochliomyia species, though 'Old World screwworm' is used analogously for Chrysomya. Eradication campaigns have eliminated C. hominivorax from North and much of Central America, but reintroduction risk remains through animal movement or climate change.