Arizona’s outdoor community can help stop this devastating pest
New World screwworm causes serious, often deadly damage to animals in areas where the pest spreads. It can also affect people causing painful, infected wounds. As long as detections and treatments are provided early, people do not typically become severely ill. While NWS is present in parts of South America — where infections in animals and people continue to occur — it was eradicated from the United States decades ago. In recent years, NWS has moved northward through Central America and Mexico and was confirmed in Texas and New Mexico in June 2026. Arizona’s outdoor community can help prevent the spread of New World screwworm. For more information and current status, visit www.screwwworm.gov.
What is new world screwworm?
New World screwworm (NWS) is the larval stage of a parasitic fly. The fly’s larvae infest open wounds and body openings, where they feed on living tissue. This devastating pest can affect livestock, pets, wildlife, occasionally birds, and in rare cases, people.
NWS flies are the size of common house flies and have orange eyes, a metallic or blue body, and three dark stripes along their back. The larva are tapered at both ends, pale with dark spine bands, and do not grow larger than 1 inch.
How Is NWS Treated and Managed?
Eradicating New World screwworm is only possible through the sterile insect technique. With this method, sterile male flies are released to mate with female NWS flies in areas of known populations, which then lay unfertilized eggs. The release of sterile flies is safe, environmentally friendly, and offers a sustainable, non-toxic alternative to chemical pesticides. It poses no risk to wildlife, livestock or people in infested areas.
The best way to protect yourself and animals from NWS is surveillance, monitoring and promptly reporting suspicions of any infestations. Infested animals should be treated according to the recommendations of a veterinarian. It’s also recommended that people avoid traveling to areas known to have NWS, do not travel with pets, and follow a veterinarian’s recommendations for antiparasictics for livestock and pets. Do not purchase and apply over-the-counter antiparasitic medications or pesticides without consulting a veterinarian.
Partners Work to Prevent the Spread
This pest was eradicated from the U.S. decades ago, but recent detections in Texas and New Mexico highlight the risk of it spreading. U.S. Agriculture Secretary Brooke Rollins introduced the New World Screwworm Domestic Readiness and Response Policy Initiative, a comprehensive five-point strategy to enhance the USDA’s already robust ability to detect, control and eliminate this pest.
The Arizona Game and Fish Department’s Wildlife Health Program is working with staff, state, federal and tribal partners, as well as researchers, rehabilitators, zoos and the public to increase awareness and preparedness.
You Can Help
As you hunt or spend time outdoors, especially near the Arizona-Mexico and Arizona-New Mexico borders, check harvested game and observe any live animals you encounter for:
- Larvae (maggots) on alive or very recently deceased animals. Unlike other maggots, New World screwworm larvae feed on living tissue, and will vacate an animal once it has died and the tissue begins to cool.
- Maggots deep in tissue with foul odor. Common sites are wounds or body openings like the nose, eyes or genitalia.
In the event that you see suspected New World screwworm:
- Take a GPS location.
- If it is wildlife, contact the Arizona Game and Fish Department immediately at 623-236-7201.
- If it is livestock, contact the Arizona Department of Agriculture at [email protected].
- Do not handle or transport the animal.
- Take pictures of the wound, larvae or affected animal, if possible.
- If you can, collect a sample safely. Using gloves and tweezers/forceps, place several larvae into a sealed container (small jar or plastic vial) with 70% alcohol. Label the container with the date, GPS location, species and your contact information. Report this immediately and submit the samples as instructed.
Your reports are critical for early detection and rapid response. Quick action could protect wildlife and livestock across the state.