Wisconsin Guidance
Effective 7/21/26: Wisconsin has regulations on warm-blooded animals entering Wisconsin from NWS infested areas. The order can be found on the DATCP website ↗️.
Contact your veterinarian for more information.
What is New World Screwworm?
New World screwworm (NWS) has been on the minds of livestock producers as it made its way north across the southern U.S. border. NWS is a parasitic fly whose larvae feed on the tissue and flesh of warm-blooded animals. The female flies deposit their eggs into open wounds and body parts such as eyes, nose, ears, and mouths. Within 12-24 hours the eggs hatch and the larvae eat the live tissue of the animal causing pain. Wounds become infected, resulting in additional discomfort, secondary health risks, and foul smells. Once larvae have fed on the host animal and are ready to molt into adults, they will drop to the ground and molt in the soil. Adult NWS flies are similar in size to house flies but are metallic blue- green with orange eyes and three dark stripes on their backs. The NWS is primarily spread via animal movement as larvae in infested animals. Adult flies do not travel very far. NWS is not a food safety concern.
How to inspect for New World Screwworm
Producers are encouraged to inspect their animals routinely for open wounds and closely look at body parts with openings. A few symptoms producers should look for in animals:
- Maggots inside open wounds, or inside the eyes, nose, ears, and mouths
- Wounds that take longer than expected to heal
- Foul-smelling odor coming from the wound site
- Excessive irritation around the wound including head shaking
- Reduced appetite
How to Prevent New World Screwworm
The greatest risk for Wisconsin producers is NWS larvae coming into the state in/on an infested animal and not being detected early.
Following a good biosecurity protocol for your farm will go a long way in keeping screwworms away. Inspect and quarantine new animals or animals returning to the farm. Remove sharp objects from animal handling and housing areas and inspect open wounds frequently. If you suspect animal disease or parasite infestations, contact your veterinarian.
Additional New World Screwworm Resources
Unified Government Response To Protect the United States ↗️ – Screwworm.gov
Animal Health Waivers & Special Orders ↗️ – State of Wisconsin Department of Agriculture, Trade and Consumer Protection (DATCP)
Strengthening biosecurity practices on dairy farms ↗️ – UW-Madison Extension Dairy Program
▶ Watch: Basic Biosecurity Practices For Livestock Operations – UW-Madison Extension Livestock Program
Holding the Line with Daily and Enhanced Biosecurity – UW-Madison Extension Livestock Program
New World screwworm (NWS) in livestock and equids: Evaluation and response ↗️– American Veterinary Medical Association
Biosecurity Resources ↗️ – Beef Quality Assurance
Eyes On Your Animals: Spot New World Screwworm (8.5×11 poster) ↗️ – Beef Quality Assurance
Protect Animal Health: Clean It Before It Travels (8.5×11 poster) ↗️ – Beef Quality Assurance
New World Screwworm Field Guide for Beef Cattle Producers ↗️ – Texas A&M AgriLife Extension