The Return of the Flesh‑Eating Screwworm: A Renewed Threat to the United States

The United States Department of Agriculture confirmed this week the first documented case of the flesh‑eating screwworm (Cochliomyia hominivorax) infecting a living mammal on American soil since the species was declared eradicated in the 1960s. The announcement marks a stark reminder that a once‑controlled biological threat can re‑emerge without warning. The screwworm larva feeds by burrowing into warm tissue, releasing proteolytic enzymes that liquefy flesh for consumption. While historically a livestock menace, the parasite can also inflict painful, potentially fatal wounds on humans, especially the immunocompromised. Its rapid life cycle—eggs hatch within 24 hours, larvae travel up to 500 km before pupation—makes containment difficult. Economic losses in the cattle industry can reach millions annually, and the ecological balance of native wildlife may be disrupted by competition with other necrophagous species. The 1960s eradication program, which employed mass releases of sterilized male flies and stringent quarantine corridors, achieved near‑total suppression across the southern United States. Its success relied on continuous surveillance and coordinated federal‑state effort. Recent climate anomalies, expanded air travel, and lax enforcement along the southern border have eroded those safeguards, allowing the fly to re‑establish populations in the Caribbean and northern Mexico, from where it can cross into Texas and beyond. Experts warn that without a renewed sterile‑insect campaign and reinforced border biosecurity, the screwworm could become entrenched, threatening ranching profitability and public health. The episode underscores the fragility of eradication achievements and the need for adaptive, science‑driven policies to prevent a resurgence that could reverberate far beyond the agricultural sector.