New World screwworm flies resurface in Texas: What livestock owners must know

The reemergence of the New World screwworm fly in the United States has triggered urgent responses from agricultural authorities, with five confirmed cases reported in Texas and New Mexico since late June. The latest detections—two in Zavala County and two in La Salle County, Texas, along with one in a dog in Lea County, New Mexico—highlight the persistent threat these parasitic insects pose to livestock health and regional economies.

While the infestation remains contained to a limited number of animals, the potential consequences are severe. The screwworm’s larvae, known for their destructive feeding habits, can burrow deep into living tissue, creating life-threatening wounds in livestock. The USDA warns that if the outbreak escalates to match past isolated flare-ups, Texas producers could face annual losses exceeding $732 million, with broader economic impacts nearing $1.8 billion. For ranchers and cattle farmers, vigilance is now more critical than ever.

How screwworm infestations spread and escalate

The New World screwworm fly (Cochliomyia hominivorax) is not a new threat. Historically, the fly was eradicated from the U.S. in the mid-20th century through aggressive sterile insect release programs. However, recent detections suggest a resurgence, likely due to cross-border movement from Mexico, where the pest remains endemic in some regions. The recent Texas cases, all involving calves, underscore how rapidly these flies can exploit livestock vulnerabilities.

The lifecycle of the screwworm is particularly alarming. Adult females lay eggs in open wounds or even unbroken skin, and within hours, the larvae hatch and begin feeding voraciously on host tissue. Left untreated, infestations can lead to secondary infections, reduced weight gain, and even death in severe cases. The dog case in New Mexico adds a layer of complexity, as the animal’s recent travel history to Mexico raises questions about the source of its infection.

Economic and ecological stakes for the cattle industry

The economic fallout from a screwworm outbreak extends far beyond individual ranches. The USDA’s economic impact assessment projects that Texas, home to one of the nation’s largest cattle industries, could bear the brunt of the damage. The $732 million annual loss figure accounts for reduced productivity, treatment costs, and trade restrictions that could follow widespread infestations. For context, the most recent significant U.S. outbreak in the 1970s triggered a $20 million eradication effort and resulted in livestock quarantines across multiple states.

Preventive measures are now in full swing. The USDA’s Animal and Plant Health Inspection Service (APHIS) has deployed rapid response teams to investigate the recent cases, enforce quarantines where necessary, and coordinate with Mexican authorities to track potential cross-border transmission routes. Ranchers are advised to inspect livestock daily for signs of infestation, including visible wounds, restlessness, or unusual behavior.

What livestock owners and veterinarians should do now

For those in affected regions, immediate action is essential. The following steps can help mitigate the risk of screwworm infestations:

• Daily inspections: Check all livestock for open wounds, unusual swelling, or signs of larvae. Early detection is key to preventing severe infestations.
• Prompt treatment: If infestation is suspected, consult a veterinarian immediately. Treatment typically involves surgical removal of larvae, followed by antibiotic and antiparasitic therapy to prevent secondary infections.
• Quarantine protocols: Isolate any affected animals to prevent the spread of larvae to healthy livestock. APHIS recommends culling severely infested animals to curb further transmission.
• Public awareness: Educate farmhands and veterinarians on recognizing screwworm symptoms, as misdiagnosis can delay critical interventions.

While human infections remain rare, the screwworm’s ability to burrow into flesh—including human skin—has drawn attention. However, health officials emphasize that the primary concern lies in livestock and the agricultural economy. The USDA urges vigilance, particularly as the flies’ resurgence coincides with peak cattle grazing seasons.

As authorities work to contain this outbreak, the cattle industry faces a pivotal moment. The next few weeks will determine whether this resurgence can be stamped out before it spirals into a full-blown crisis. For ranchers, the message is clear: act swiftly, prioritize prevention, and collaborate with agricultural agencies to safeguard both animals and livelihoods.