(Cochliomyia hominivorax)
New World screwworm (NWS) is a devastating pest of livestock that can affect any warm-blooded animal and rarely people. This pest does not impact food safety. The beef, pork, chicken, and dairy products sold in the U.S. remain safe to eat. On June 2, 2026, USDA Animal and Plant Health Inspection Services (APHIS) confirmed the first detection of New World Screwworm larvae in the United States since 1966.
For the most recent updates on NWS in the United States, visit: www.screwworm.gov
Animal movement requirements for animals entering Pennsylvania: PA Notice of NWS Animal Movement Requirements
The NWS is a fly species that was eradicated from the U.S. in the 1960’s, but was still present in Central and South America. It began moving northward in 2023, but remained outside the U.S. until 2026. The NWS is different from common fly species in Pennsylvania because the larvae of the NWS feed on living tissue, while larvae of fly species commonly found in Pennsylvania feed on dead tissue or organic matter. NWS flies will lay eggs on any wound, even very small wounds, including:
The feeding of NWS larvae cause the wounds to enlarge and continue to worsen. There may also be secondary infections present in the wound. NWS can affect livestock, pets, wildlife, occasionally birds, and in rare cases, people. Animals with NWS infestations may show signs of infection including:
Although untreated NWS infestations can be fatal, there are treatments available that can allow infested animals to recover. In the event of a case of NWS in Pennsylvania, the Department of Agriculture would work with USDA to ensure affected animals are treated for the infestation and surrounding areas are monitored closely for presence of the NWS fly or other infested animals.
If you suspect signs of NWS in your animals, call your local veterinarian, report it to the State veterinarian’s office (717-772-2852), or report it to USDA (www.aphis.usda.gov/contact/animal-health).
For more information about screwworm, including information on the NWS outbreak please visit the following websites.