CDFA - AHFSS - New World Screwworm

New World Screwworm Alert

New World Screwworm Confirmed in Five Cases

SACRAMENTO, CA - June 8, 2026, the United States Department of Agriculture (USDA) Animal and Plant Health Inspection Service (APHIS) confirmed a total of four (4) cases of New World Screwworm (NWS), two calves in Zavala County, Texas, one calf in La Salle County, Texas, a goat in Gillespie County, Texas, and a dog in Lea County, New Mexico. USDA has activated the sterile fly dispersal facility at Moore Air Base in Edinburg, Texas and continues to release sterile flies infested and surrounding areas.

CA SITUATION STATUS

At this time, there are NO confirmed detections of New World Screwworm in California. CDFA is coordinating closely with USDA APHIS and neighboring state animal health officials to monitor the situation. All California dairies and livestock operations are encouraged to maintain vigilance. NWS is not a food safety concern. For national NWS detection data, visit the USDA APHIS website.

In addition to CDFA's fly trapping efforts to monitor NWS at California’s border, CDFA is updating animal importation requirements entering the state from known infected zones

REPORTING SUSPICIOUS CASES

California animal owners and veterinarians should monitor for draining or enlarging wounds, fly egg or maggot infestations, and lesions around body openings (ears, nose, genital area, umbilicus). All suspicious cases should be reported to CDFA immediately at 866-922-2473.

While not common in people, if you notice a suspicious lesion on your body or suspect you may have contracted screwworm, seek immediate medical attention.

INQUIRIES

For public inquiries regarding New World Screwworm in California, please send an e-mail to NWSinfo@cdfa.ca.gov or call 866-922-2473.

For media inquiries, please call 916-654-0462 or send an e-mail to OfficeOfPublicAffairs@cdfa.ca.gov.

New World Screwworm Confirmed in Texas

SACRAMENTO, CA - June 4, 2026: June 4, 2026: The California Department of Food & Agriculture (CDFA) Animal Health Branch is issuing this notification in response to a confirmed detection of New World Screwworm (Cochliomyia hominivorax) in the United States.

On June 3, 2026, the United States Department of Agriculture (USDA) Animal and Plant Health Inspection Service (APHIS) confirmed the presence of New World Screwworm (NWS) in Zavala County, Texas. The affected animal is a 3-week-old calf and larvae were identified in its umbilical area. This is the first confirmed detection of NWS in animals in the continental United States since the parasite was eradicated from the U.S.

CA SITUATION STATUS

For national NWS detection data, visit the USDA APHIS website.

BACKGROUND

New World Screwworm is a devastating parasitic fly whose larvae (maggots) infest the open wounds of warm-blooded animals, including livestock and wildlife, and in rare cases, humans. Unlike common blow flies, NWS larvae feed on living tissue, which can be fatal if untreated. NWS had been eradicated from the United States, Canada, and Mexico through a sustained sterile insect technique (SIT) program operated by USDA APHIS and partner agencies.

California has significant livestock and wildlife populations at risk. The re-introduction of NWS into the United States represents a serious threat to the agricultural economy and animal welfare.

REPORTING SUSPICIOUS CASES

While not common in people, if you notice a suspicious lesion on your body or suspect you may have contracted screwworm, seek immediate medical attention.

INQUIRIES

For public inquiries regarding New World Screwworm in California, please send an e-mail to NWSinfo@cdfa.ca.gov or call 866-922-2473.

For media inquiries, please call 916-654-0462 or send an e-mail to OfficeOfPublicAffairs@cdfa.ca.gov.

Identification

Reporting

Resources

Screwworms are fly larvae (maggots) that feed on living flesh. These parasites can infect any warm-blooded animal. Screwworms enter wounds as small as a tick-bite and feed on living tissue in the area. If untreated, screwworm infestations can be fatal. In the US, Screwworm is a Foreign Animal Disease reportable within 24 hours of diagnosis. Screwworms have most recently entered the US in dogs that have been imported from areas of the world where the flies are endemic.

New World screwworm, Cochliomyia hominivorax, has been moving North again after years of being pushed down past the Darién Gap in Panama. While endemic in many regions of South America and some Caribbean Islands, the screwworm was recently found in Nuevo Leon, Mexico which is 70 miles off the US border.

While an adult screwworm fly is capable of flying for up to 10-14 days, they typically only fly short distances, 6-9 miles (10-15 km) when there are sufficient hosts in the area and suitable environmental conditions. Although the screwworm fly is capable of flying up to 125 miles, longer distance spread is more likely facilitated and propagated via transport on human and animal hosts.

Identification

New World Screwworm Larvae

Zoom

Pale with encircling black spines
No head capsule
Long tapered appearance

Immature Larvae

Larvae in myiasis cases may be recognized by the shape of their spiracles
- Number of slits = instar
- Sclerotized peritreme
- Button
Positioning of tubercles
Spines at segment margins

	New World Screwworm Cochliomyia hominivorax	Secondary Screwworm Cochliomyia macellaria
Distribution	Americas and Caribbean	Americas and Caribbean
Abundance	Low densities in the environment	Common/abundant in the environment
Climate	Warm-temperate to tropical	Temperate to tropical
Feeding habit	Living, warm-blooded animals	Carrion, rarely living animals
Importance	Parasite of: Livestock Wildlife Pets Humans	Decomposer Forensics/time of death Pollinator Live animal infestation is rare



Adult Screwworm Flies

Infested animals may present with enlarging, draining, foul-smelling wounds and weight loss; they may isolate themselves and show signs of discomfort. Animals may die from secondary infection or toxicity in 7-14 days if not treated.

Wounds that might become infested include those caused by: Tick bites, castration or dehorning, branding, shearing, and sore mouth in sheep.

In addition, screwworms can infest the navels of newborn mammals, and mucous membranes of bodily orifices, including: nostrils and sinuses, eyes, mouth, ears, vulva, anus, prepuce, and urethral fossa.

Photo: head of deer infested with screwworms

A deer's head infested with screwworms

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Reporting

Screwworm infestation is a foreign animal disease and must be reported to CDFA or USDA animal health officials within 24 hours of diagnosis or suspicion for all livestock and pet.

Samples of eggs, larvae, or flies should be placed in 70% ethanol or isopropyl alcohol for transportation to the diagnostic laboratory.

Animal Health and Food Safety Services

Animal Health Branch

Headquarters

Redding District

Modesto District

Tulare District

Ontario District