06/09/2026
The New World Screwworm (NWS) is all over the news right now, and we’ve received a lot of questions from livestock owners and animal caretakers.
We think it’s important to share some facts published by USDA about New World Screwworm and what it means for animal owners.
And while most of those discussions have focused on cattle—and for good reason. Cattle are certainly at risk. But they’re not the only animals we need to be talking about. As we heard yesterday, now a dog from New Mexico with some recent travel has also tested positive in Texas.
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What animals can be affected by New World Screwworm?
The answer: Any warm-blooded animal can be affected.
That includes:
• Cattle
• Horses
• Sheep and goats
• Swine
• Dogs and cats
• Wildlife
• And, in rare cases, people
🪰 What is New World Screwworm?
New World Screwworm (NWS, Cochliomyia hominivorax) is a serious pest that can affect livestock, pets, wildlife, and, less commonly, people and birds.
Adult screwworm flies are about the size of a common housefly or slightly larger. The concern is not the adult fly itself, but the larvae (maggots), which feed on the living tissue of warm-blooded animals.
🪰 How does it spread?
NWS is not contagious. It does not spread directly from animal to animal, animal to person, or person to person.
Infestations begin when a female fly lays eggs in a wound or body opening. The eggs hatch into larvae that feed in the wound. After several days, the larvae drop to the ground, pupate in the soil, and eventually emerge as adult flies, continuing the cycle.
🐄 Will animals be culled?
According to USDA, culling is not expected to be used to manage livestock diagnosed with NWS.
Animals with suspected infestations will be evaluated, treated, and quarantined until wounds have healed and there is no evidence of reinfestation. In rare cases, euthanasia may be necessary for humane reasons or when treatment is not possible.
⚠️ Not all maggots are New World Screwworm.
Myiasis is the infestation of tissue by fly larvae (maggots). While NWS can cause myiasis, other flies—including botflies and blowflies—can also produce similar infestations.
Because of this, the presence of maggots alone does not confirm NWS. Identification by an entomologist is required to determine the species involved.
🔎 What should you watch for?
• Maggots or white egg masses in wounds or body openings
• Wounds involving the nose, ears, eyes, ge***alia, or navels of newborn animals
• A foul odor or smell of decay
• Irritated behavior or signs of pain
• Depression or lethargy
• Loss of appetite
• Animals isolating themselves from people or other animals
📞 If you observe suspicious wounds or maggots on an animal, contact your veterinarian immediately.
It is also important to note, lots of changes is already happening regarding animal movement out of Texas and out of the infected zones.
As information continues to evolve, we’ll keep sharing updates and educational information to help animal owners stay informed.
