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Fly Strike

Myiasis, Fly Blown


New World Screwworm Myiasis, commonly referred to as "Fly strike", is a disease affecting chickens and other livestock that's caused by infection with the New World Screwworm, Cochliomyia hominivorax. The adult screwworms seek out susceptible hosts, consisting of chickens with open wounds, and lay their eggs inside. Screwworms reproduce extremely fast---the eggs only require 8 to 12 hours to hatch. As the eggs hatch, the developing larvae eat on the flesh from the wound and surrounding tissue of the chicken, resulting in severe tissue damage, increased risk of secondary bacterial infections, and often painful death.

In late September 2016, the U.S. Department of Agriculture’s Animal and Plant Health Inspection Service (USDA APHIS) National Veterinary Services Laboratories confirmed the presence of New World screwworm in infected Key deer (Odocoileus virgineanus clavium) from National Key Deer Refuge on Big Pine Key, Florida. The New World Screwworm was thought to have been successfully eradicated 50 years ago, due to efforts made by the USDA in the 1950s and 60s.

Clinical Signs

Presence of eggs or moving insects in a wound


  • History
  • Clinical signs
  • Physical exam
  • Laboratory tests


Supportive careIsolate the bird from the flock and place in a safe, comfortable, warm location (your own chicken "intensive care unit") with easy access to water and food. Limit stress. Call your veterinarian.
Wound careClean and flush wound (making sure to remove all eggs and maggots)
AntibioticsMay be indicated for secondary infections.


  • Practice good fly control
  • Conduct daily inspects of all flock members
  • Keep chicken's bottoms clean and free of feces
  • Promptly treat any open wounds

Scientific References


Risk Factors

  • High fly populations
  • Chickens with missing feathers/bare patches of exposed skin