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Screwworm Reappears in U.S., Tracked in South Texas and New Mexico

Officials say a shortfall in sterile‑fly supply is the key obstacle to stopping the parasite.

The Novofly could revolutionize the fight against screwworm by making sterilization more efficient and effective (USDA)
Carrizo Springs rancher Bill Martin explains what it takes to make sure his cattle are safe from screwworm
Researchers at the Knipling-Bushland U.S. Livestock Insects Research Laboratory in Kerrville are developing a male-only strain of sterile New World screwworm flies designed to improve eradication efforts. (SBG San Antonio)
Zamira Yusseff shows us how scientists compare screwworm to other types of larvae to confirm its presence in animals (SBG San Antonio)

Overview

  • The New World screwworm was first detected in South Texas in June 2026 and, as of July 23, cases have been found beyond the initial zone including at least one dog in New Mexico.
  • USDA and partners have reopened and expanded sterile‑fly programs, using releases from Metapa, a new dispersal site at Moore Air Base, and a U.S. plant under construction, but current production lags the modeled number of sterile males needed.
  • Researchers are developing a male‑only sterile strain called Novofly that could roughly double the number of useful sterile males, but it requires field trials and federal regulatory approval before it can be used in the field.
  • The USDA has awarded roughly $105 million for research projects, including Colorado State University studies of wound‑volatile chemicals to create lures that more specifically attract New World screwworm and faster diagnostics to speed detection.
  • Ranchers and states have tightened biosecurity—movement certificates and inspections are in effect—and officials warn wildlife reservoirs, slower production scale‑up, and months of regulatory review could prolong control efforts and raise costs for livestock producers.