Keep Minnesota’s animals safe from New World Screwworm
St. Paul, Minn. - Minnesotans are asked to stay alert for New World Screwworm (NWS), a fly that lays a destructive maggot capable of inflicting great harm on livestock, pets, wildlife, and on rare occasion, humans. The U.S. Department of Agriculture is also working to strengthen measures to keep the pest out of the U.S. While the risk is lower for this parasite to become established in Minnesota compared to southern states, introductions are still possible due to international animal movements. The Minnesota Board of Animal Health prioritizes staying vigilant for NWS and other invasive pests and diseases. Threats like NWS can move quickly and unintentionally on animals.
“Currently there are outbreaks of NWS in Central America and detections in Mexico,” said State Veterinarian Dr. Brian Hoefs. “Many people falsely think our northern climate is a strong enough deterrent to tropical pests like NWS. Unfortunately, our summers and shoulder seasons are warm enough to allow this fly to complete its lifecycle and potentially spread in Minnesota.”
NWS is an old threat that used to be endemic in the United States until an eradication program was started in the 1950’s and drove it down to Central America by the 1980’s. With new threats emerging of a resurgence of this pest in 2025, it’s important for livestock owners, travelers, pet owners and others to work together to keep it from spreading, especially into the U.S.
Learn the signs of screwworm infestation and report suspected cases to a veterinarian immediately. Telltale signs include open wounds with maggots, strong odor, irritated animal behavior, and tissue decay that expands and deepens over time. Infested animals usually separate from the herd and lie down and will have visible discomfort, or decreased appetite.
The best way to reduce the risk of NWS for Minnesota’s animals is to keep it out of the state in the first place. If you’re traveling with pets, you must follow all import requirements, which are designed to screen for diseases and pests like NWS. You know your pet best, so it’s also a good idea to look it over for any signs of illness and report concerns to animal health authorities. Once you return home you should check in with your regular veterinarian about your travel and any concerns you have about your pet. Check the status of the destination country for NWS and other parasites and diseases of concern. Consider not including your pet on trips to high risk areas.
More questions about NWS and where it is in the world? Follow resources from our partners at the USDA where they track national progress on monitoring and repelling this pest.
Additional resources: