06/17/2026
New World screwworm (NWS) has been detected in the U.S. This flesh-eating parasite can be devastating to animals and people. Review this guide to learn how to monitor your animals, what to look for, and why quick action and strict compliance with prevention protocols are so important.
What is the New World Screwworm?
The New World Screwworm (Cochliomyia hominivorax) is a dangerous parasite that feeds on the living flesh of warm-blooded animals (including livestock, wildlife, pets, and rarely humans). Unlike common maggots that feed only on dead tissue, NWS larvae will consume healthy living skin and muscle, causing severe wounds and potential death if left untreated.
What to Look For:
Early detection is critical to stopping the spread and protecting your animals. Please monitor your animals closely, paying special attention to:
• Open Wounds: Check for draining, foul-smelling, or enlarging lesions.
• Body Openings: Look for egg masses or maggots in and around the ears, nose, eyes, mouth, and ge****ls.
• Newborns: Closely check the navel area of any newly born animals.
• Signs of Discomfort: Watch for unusual irritability, restlessness, or animals scratching at specific spots on their bodies.
How to Protect Your Herd or Pets:
• Year-Round Prevention: Ensure your pets and livestock are on an aggressive, year-round ectoparasite (flea and tick) control program.
• Wound Management: Treat any open wounds promptly. If you have recently branded, dehorned, or castrated animals, keep them in clean environments and observe them for fly attraction.
• Travel Caution: Be extremely cautious with animals traveling to and from affected or high-risk regions. Currently, the export of cattle, horses, sheep, goats, swine, dogs, ferrets and many birds to Mexico is restricted.
What to Do If You Suspect an Infestation:
Because NWS is a highly destructive and reportable pest, immediate action is required by law. Do not attempt to treat the animal yourself.
Please contact our hospital immediately. For the latest updates on detection zones and federal/state regulations, please visit the
USDA APHIS Screwworm Resource Center.
Your vigilance is our first line of defense. Please do not hesitate to reach out to the hospital if you have questions about current parasite control medications, need to schedule a routine check-up, or want to discuss risk factors for your specific operation or household.
