The flesh-eating New World screwworm is back in the U.S. — and spreading fast

The New World screwworm, a parasitic fly whose larvae feed on living tissue, has re-emerged in the United States after decades of absence. Once eradicated through a landmark biological control campaign in the 1950s, the pest has now been confirmed in Texas and New Mexico, raising urgent concerns for livestock, wildlife, pets — and occasionally, people.

To get ahead of the threat, researchers at UC San Diego and the County of San Diego's Public Health Services developed a real-time risk tracking dashboard. The tool integrates confirmed detections, environmental data, and even news media reports — which can surface early warning signals before official lab confirmations (which can take days or weeks) catch up.

The USDA is leading the eradication response, combining sterile insect releases, pesticides, and animal movement quarantines. Officials are also seeking EPA approval for a genetically modified all-male fly strain to bolster control efforts.

Key Takeaways:

• Screwworm larvae enter open wounds or body openings and burrow into healthy tissue — without treatment, infestations can be fatal to animals
• The parasite does not spread person-to-person, but humans can be infected through wound or mucous membrane exposure
• The dashboard, part of the CDC-funded Insight Net network, is currently available to public health officials with a public version planned
• Adult flies can travel miles on their own; infected animals can also carry the parasite into new regions

Why it matters: The screwworm's rapid northward spread caught even experts off guard. With the right tracking tools and a proven eradication playbook, officials have a fighting chance — but the window to act is narrow.