Cochliomyia hominivorax: American Screwworm fly (Callitroga hominivorax).

General Description: An adult fly about 10 - 15 mm. Long with a metallic blue body and a reddish-orange face. There are 3 dark stripes on the dorsal surface of the thorax. The mature larvae are about 12 mm long; the paired tracheae are pigmented. The palps are short and thread-like and the antennae are feathered to the tips.

Life Cycle: The female lays batches of 200 - 300 eggs in compact masses at the edge of a wound on the host. Eggs hatch in ½ to 1 day and the larvae grow to maturity in 3 - 6 days. The larvae feed in a characteristic head-downward position with the spiracles pointing toward the opening of the wound. When mature, the larvae drop to the ground and pupate. The pupal period can last from several days to several weeks depending on the prevailing temperature.

Location: Living tissue and fresh lesions.

Geographical Distribution: North and South America.

Significance: Prior to the program of mass sterilization of female flies, annual losses of many million dollars were reported in the US livestock industry.

Effect on Host: Flies deposit eggs in fresh wounds. The developing maggots penetrate into tissues which they liquidize. The wound becomes foul; death may follow if the animal is not treated.

Diagnostic Information: The adult flies or larvae must be identified.

Control: Treat infestation to kill the larvae; avoid creating wounds during the fly season. Inspect animals more frequently. Management practices such as castration, dehorning, docking and branding should be conducted in cool weather. Plan breeding so that young animals are not born in fly season. Practice fly and tick control.

Adult fly		Screwworm fly larvae
Screwworm fly larvae in lesion		Larvae at gum line