06/08/2026
TL;DR screwworm has been found in southern Texas. The larvae of the new world screwworm eat living tissue (unlike other maggots), causing a VERY bad smell. If you think you have screwworm in your livestock (or your pets or yourself), please call because that would be a big deal. Read more at screwworm.gov.
As you may have already heard, New World screwworm was found in a calf in South Texas (Zavala County) late last week. These flies (yes, confusing, wet know) lay eggs into open wounds (surgery/castration/tail docking sites, newborn umbilical cords, etc.) and body openings (eyes, ears, nose, mouth, genitalia) that hatch into parasitic maggots that burrow into and feed on living tissue or flesh. This can happen in any warm-blooded animal including cattle, sheep, goats, pigs, horses, dogs, cats, and, rarely, humans.
In Texas, the federal government is working on capturing flies and has released sterile female flies to hopefully distract and breed the males, breaking the cycle. We have eliminated this parasite from the country in the past and can do it again.
What you can do: if you are castrating or notice wounds, fly/maggot control is extremely important. We routinely recommend CATRON IV spray to avoid maggots in wounds at the time of castration and this spray is labelled to prevent screwworm 🙂 While an antibiotic (like penicillin) may help with an infection, it will NOT prevent screwworm. You need a fly preventative.
There are more preventative measures found in the link below that have been approved for use in different species. Please don’t hesitate to call your vet if you’re concerned you’ve found screwworm or have ANY questions.
UNHS Hooves and Hands’s hooved animal veterinarian Dr. Magdalena Niedermeyer can be reached at 435-320-0377.
More resources:
Utah Department of Agriculture Update Video (4min) (https://www.youtube.com/watch?v=ftnWuGqjpP8)
UT Reporting Form and other Info (https://ag.utah.gov/animal-industry/animal-health-program/new-world-screwworm/)
The USDA/APHIS Announcement (https://www.aphis.usda.gov/news/agency-announcements/usda-confirms-presence-new-world-screwworm-united-states)
FDA Approved Prevention/Treatment for Screwworm (https://www.fda.gov/animal-veterinary/safety-health/new-world-screwworm-information-veterinarians)