The New World screwworm (Cochliomyia hominivorax) has re-emerged, having been eradicated in the United States since the 1960s. According to Agriculture Secretary Brooke Rollins, this resurgence is linked to the current administration's “open border policies.”

Donald Trump officials have pointed directly to former President Joe Biden's immigration policies as the root cause. “The threat did not arise overnight; it was a direct result of the weak foreign policy agenda and failed immigration policies of the Biden-Harris administration,” Rollins wrote in a social media post, reported by The Hill.

The parasitic fly, which feeds on living and undead matter, has begun to affect livestock again in Texas and New Mexico. Currently, there are five confirmed cases, including a dog in the state of New Mexico.

Historically, the screwworm was contained in Panama through a program that released sterile male flies. However, the spread has gained ground in recent years, reaching Mexico in 2024, after the flies surpassed the insect barrier and the Darién Gap by 2022.

Response from current administration

The Biden administration took immediate action, closing ports of entry to prevent the entry of infected livestock following confirmation of cases in Mexico. However, this decision was reversed by President Trump, generating controversy in the livestock sector, notes The Hill.

Despite the staff cuts at the Department of Agriculture, Rollins assures that the response has not been affected. The administration has named John Bellinger as an advisor on screwworm preparedness and has initiated the opening of new facilities for the production of sterile flies.

The experts speak

Entomology specialists warn that the important thing now is to act effectively to contain the problem. Although the return of the screwworm has been rapid, reestablishing areas free of this parasite will take significant time and resources, such as the production of sterile flies.

With the only sterile fly production plant in Panama, there is a recognized insufficiency in the capacity to counteract the infestation. The current administration has initiated efforts to correct this lack, but the effectiveness of these efforts remains to be seen.

This resurgence and the political disputes around it show the complexity of the measures necessary to avoid future livestock crises in the United States.

How the screwworm works

The name screwworm, or New World screwfly (NWS), refers to the way the larvae curl into animal tissues with their sharp mouth hooks, causing extensive damage, including death.

The female deposits her eggs in open wounds or body orifices; The larvae hatch and burrow into the meat, which can be fatal within weeks if untreated, explains the Centers for Disease Control and Prevention (CDC). A single female fly can lay between 200 and 300 eggs at a time and can lay up to 3,000 eggs during her 10- to 30-day life cycle.

The eggs hatch, giving rise to larvae that enter the wound to feed on living tissue. After feeding for about 7 days, the larvae fall to the ground, bury themselves, and emerge as adult borer flies. That's the cycle.

It is valid to note that most infestations occur in animals, but also in people.

In August 2025, the United States reported the first human case of NWS in the country, in an international traveler. The individual recovered and there was no evidence of subsequent spread, ABC News reported.

The presence of the New World screwworm has so far been detected mainly in the state of Texas and New Mexico.

Prevention

Preventing skin wounds and avoiding NWS flies is essential to protect yourself in areas where these flies are present. The CDC recommends:

Treatment

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