Jun 16, 2026 By Karen Mansfield 2 min read

The Pennsylvania Department of Agriculture announced it is issuing a quarantine order to limit animal movement and tighten biosecurity amid the rising risk of New World Screwworm.

Secretary Russell Redding said that farmers must protect their livestock after cases of NWS have been reported in Texas and New Mexico.

“Pennsylvania has no confirmed cases of New World Screwworm, but this destructive pest poses a serious threat to our livestock industry, companion animals, wildlife, and agricultural economy,” Redding said. “Taking proactive steps now to strengthen biosecurity and limit unnecessary animal movements from affected areas will help protect our farms and communities.”

The screwworm is a devastating pest. When NWS fly larvae – maggots – burrow into the flesh of a living animal, they cause serious, often deadly damage. NWS can infest livestock, pets, wildlife, occasionally birds, and in rare cases, people.

“New World Screwworm is unlike the flies and maggots we commonly encounter,” said state veterinarian Dr. Alex Hamberg. “These larvae feed on living tissue, causing severe wounds that can quickly become life-threatening if left untreated. Producers, veterinarians, and pet owners should regularly inspect animals for wounds that fail to heal or show signs of maggot infestation. If producers suspect NWS, they should seek veterinary care immediately.”

Pennsylvania’s quarantine order, which took effect on June 9, establishes movement restrictions and enhanced animal health requirements for susceptible domestic animals entering Pennsylvania from affected areas. The order includes provisions for veterinary inspection, animal health certification, and preventative measures designed to reduce the risk of NWS entering the commonwealth through animal movements.

Pennsylvanians are advised to monitor their livestock and pets for the signs such as irritated behavior, head shaking, the smell of decay, and the presence of maggots in wounds.

Adult screwworm flies are about the size of a common housefly or slightly larger. They have orange eyes, a metallic blue or green body, and three dark stripes along their backs.

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 ulceration or tear in the skin or mucous membranes.

Anyone who suspects a screwworm infestation should immediately contact their veterinarian and report the suspected case to the Pennsylvania Department of Agriculture’s Bureau of Animal Health and Diagnostic Services at 717-772-2852.