US, Mexico Drop 100 Million Sterile Flies as Illegal Cattle Routes Drive Screwworm North
Updated
Updated · The Guardian · Jul 12
US, Mexico Drop 100 Million Sterile Flies as Illegal Cattle Routes Drive Screwworm North
3 articles · Updated · The Guardian · Jul 12
Summary
100 million sterile flies are being released across the US Southwest and Mexico to slow the new world screwworm, after the parasite was detected in 34 US animals—mostly in Texas and one in New Mexico.
Experts say that volume can curb northward spread but not eradicate the pest; pushing it back south would require about 500 million flies, with a new Mexico facility opened in late June and a Texas plant due in late 2027.
Camera traps in Central American forests found jaguars, tapirs, deer and other wildlife infected far from cattle sites, suggesting the fly is now endemic in wildlife and harder to contain.
Researchers say the rapid advance followed illegal cattle-trafficking routes: after crossing the Darién Gap in 2022, the screwworm shot from Nicaragua through Central America within four to five months, effectively moving at truck speed.
That pattern has widened concern beyond screwworm to other livestock-borne diseases, with conservationists warning that unchecked cross-border animal movement leaves the region vulnerable while US research capacity is only now being rebuilt.
As sterile flies offer a temporary fix, can the US halt the illegal cattle trade fueling this screwworm invasion?
A 50-year research ban left the US vulnerable. Can new gene-editing tech now stop the screwworm plague for good?
The screwworm is killing jaguars and pumas. Is the current response ignoring the ecological crisis at its source?
New World Screwworm Outbreak 2026: U.S. Faces Livestock Crisis Amid Illegal Trade and Biosecurity Gaps
Overview
The re-emergence of the New World screwworm (NWS) in Texas and New Mexico in July 2026 has triggered an immediate and coordinated response from U.S. and Mexican authorities. Recognized as a serious threat to rural and ranching communities, the outbreak has raised concerns among lawmakers, especially in Colorado, about the risk of catastrophic infestations if surveillance is not strengthened. The USDA is leading a One Health approach, focusing on robust surveillance and inspections, while lawmakers are calling for enhanced efforts across affected states. Prompt reporting of suspected cases is emphasized as a key step in controlling the spread and protecting animal health.