New World Screwworm

There are currently no cases of New World screwworm in Pennsylvania in livestock, pets, wildlife, or humans.

The Pennsylvania Department of Agriculture has issued a quarantine order limiting animal movements and is urging Pennsylvania farmers and pet owners to tighten biosecurity to protect their livestock and pets following heightened risks of New World Screwworm (NWS) following confirmed cases in Texas and New Mexico. 

The risk remains low, but animal owners should remain vigilant and report suspicious wounds containing larvae in livestock, pets, or other warm-blooded animals. Maggots found in the environment, such as in trash or decaying organic matter, are not indicative of NWS. The Pennsylvania Department of Agriculture and its partners are monitoring the situation closely, but the Commonwealth remains free of the parasite.

NWS is not an environmental maggot. The larvae develop only in the living tissue of warm-blooded animals, typically entering through an open wound or natural body opening. Finding maggots in garbage, compost, or dead organic matter is not consistent with NWS.  

Pennsylvania livestock owners, veterinarians, and animal owners are encouraged to watch for unusual wounds that contain live larvae and report suspected cases promptly. Early detection is essential to preventing establishment of the parasite.  
 

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.

• Unified Government website for most accurate and up-to-date NWS information

• USDA New World Screwworm Playbook and Supplemental materials

• U.S. Food and Drug Administration (FDA) Animal Drugs for New World Screwworm

• USDA APHIS Pesticides for Control of New World Screwworm

New World screwworm larvae develop in the wounds of warm-blooded animals, they are not found living freely in yards, trash cans, or other environmental materials. The public should report suspected cases involving larvae in an animal’s wound, rather than isolated maggots found in the environment. Reports involving domestic animals should be directed to your local veterinarian or the Bureau of Animal Health and Diagnostic Services.
 

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, click here. 

The recent U.S. detections have been limited to Texas and New Mexico, where federal and state officials are conducting surveillance, quarantines, and sterile fly releases to contain the pest.  
 

The NWS is a fly species that was eradicated from the U.S. in the 1960s 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: 

• Cuts and scrapes, 

• Umbilical stumps

• Castration or other surgical wounds

• Ear tag sites

• Mucous membranes

• Wounds as small as a tick bite

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: 

• Worsening, enlarging wounds

• Lethargy, weakness

• Not eating/drinking

• Presence of maggots

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.