How to identify it
- Adults are metallic flies with three distinct stripes running back from behind the head, the middle stripe shorter.[1]
- Larvae are about 17 mm long, with rings of spines that look almost screw-like; a trained professional must confirm the species.[1]
- Infested wounds hold visible maggots, often smell foul and drain or enlarge.[1][2]
Look-alikes
| Look-alike | How to tell them apart |
|---|---|
| Secondary screwworm | Cochliomyia macellaria looks similar, but its back stripes are more even; it and other metallic blow flies lay eggs only on dead tissue.[1] |
Where it lives
Eradicated from the US by the mid-1960s with sterile flies, it re-emerged in Central America and southern Mexico, reached Nuevo León by September 2025, and USDA confirmed cases in La Salle and Andrews counties, Texas, on June 8, 2026.[1][2]
Biology and life cycle
Mated females are drawn to wounds as small as a tick bite or a barbed-wire scrape and can travel 6 to 12 miles to find one.[1]
Females lay 100 to 300 eggs that hatch in 6 to 8 hours, and the larvae feed for 5 to 7 days in living tissue before pupating in soil.[1]
Adult males live 3 to 4 weeks and feed on nectar; females live about 1 to 3 weeks.[1]
Damage and signs
Health risk
Infestations in people are rare; USDA advises anyone who notices a suspicious lesion to seek immediate medical care.[2]
Control
Prevention
Check animals often for draining or enlarging wounds, maggots or egg masses, signs of discomfort, and lesions in the nose, ears, genitals or navel.[2]
Treat wounds promptly; if an infestation occurs, cleaning out the maggots and topical larvicides such as permethrin are control options, guided by a veterinarian.[1]
When to call a professional
Report suspected cases right away to your veterinarian, state animal health official or USDA; in Texas, report livestock cases to the Texas Animal Health Commission.[2]
USDA fights outbreaks with 20 km quarantine zones and releases of sterile flies, which are dyed so trap catches can be told apart from wild flies.[2]
Status as of October 2026
As of October 4, 2026, USDA had confirmed 53 cases in animals since June, 51 in Texas and 2 in New Mexico, with three still active; a wild screwworm fly was also caught in a surveillance trap in Brewster County, Texas, on September 25.[3]
Common questions
- Is the New World screwworm in the United States?
- Yes. USDA confirmed cases in La Salle and Andrews counties, Texas, in June 2026, including a dog that early reports said had recently been in Mexico.[2]
- Can screwworm get into meat or produce?
- No. USDA says it doesn't infest meat, fruits, vegetables or other food products.[2]
- What should I do if I see maggots in an animal's wound?
- Contact your veterinarian, state animal health official or USDA immediately.[2]
Sources
- Penn State Extension, “Understanding the New World Screwworm: Biology, Identification, and Prevention (updated October 24, 2025).” extension.psu.edu/understanding-the-new-world-screwworm-biology-identification-and-prevention (accessed 2026-10-06)
- USDA Animal and Plant Health Inspection Service, “USDA Confirms Two Additional Cases of New World Screwworm in the United States (June 8, 2026).” www.aphis.usda.gov/print/pdf/node/8171 (accessed 2026-10-06)
- Texas Public Radio (USDA data), “New World screwworm cases climb to 53; new case confirmed in Brewster County dog.” www.tpr.org/public-health/2026-07-03/31-confirmed-new-world-screwworm-infestations-texas-tracker-and-what-you-need-to-know (accessed 2026-10-15)
- iNaturalist, “Cochliomyia hominivorax taxon page (order and family).” www.inaturalist.org/taxa/354351 (accessed 2026-10-06)