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Government · Agriculture

The Fly War Was Won. Then We Closed the Factory.

America eradicated the flesh-eating screwworm decades ago with one biological insight. The parasite returned after the infrastructure that maintained the win was quietly dismantled.

By the Fuxed Desk • 6 min read • Severity ★★★★★ Severe
What wasn’t broken
For about forty years, a continental barrier of sterile male flies held the New World screwworm — a blowfly whose larvae eat living tissue — south of the Darién Gap. The method used no pesticide and exploited one fact: female screwworms mate only once.
The "fix"
As the parasite receded from memory, the production infrastructure was retired. The Mexican mass-rearing plant — once making 550 million sterile flies a week — closed in 2012 for economic reasons, leaving a single aging Panama facility as the hemisphere’s main defense.
The result
After COVID-era disruptions, detections in Panama jumped from ~25 to over 6,500 cases in 2023. The parasite reached Mexico in late 2024 and Texas by June 2026. The federal response: a $610 million emergency fly factory — replacing one that already existed. Fuxed

The screwworm was, as eradication stories go, unusually legible. Scientists found the vulnerability — females mate once and store sperm for life — and flooded the population with sterilized males.1 Mate enough females with sterile males and the population collapses. By 1966 the continental United States was declared free of it; by 2006 a biological barrier at Panama’s Darién Gap released about 100 million sterile flies a week to keep it that way.1

The barrier held because it was maintained — and it was expensive. As the screwworm faded from institutional memory, so did the appetite to fund it. Facilities closed one by one. Experts had warned that depending on a single Panama plant made another incursion inevitable.2 The Mexican plant at Tuxtla Gutiérrez, which at peak produced 550 million sterile flies a week, was shuttered in 2012 as an economic decision.3

The pandemic is widely cited as the proximate trigger, disrupting production and surveillance at the Panama facility during 2020–2022. In 2023, Panama detections rose from roughly 25 to more than 6,500. The parasite moved through Central America and entered Mexico in late 2024.1

The primary U.S. response was to stop importing the animals it might travel with. On May 11, 2025, the USDA suspended live cattle, horse, and bison imports across the southern border, effective immediately.5 It did not stop the spread. Beef prices — already up sharply since 2019 — faced further pressure.6 On June 3, 2026, the parasite was confirmed in a three-week-old calf in Zavala County, Texas, ending a domestic-freedom record that had stood since the 1960s.7

The emergency response now includes a $610 million sterile-fly production facility in Edinburg, Texas — the same function a shuttered plant once performed for a fraction of the cost.4 Separately, the agency responsible for border animal inspections lost about 2,009 employees — 23% of its workforce — in the fourteen months before the Texas detection; critics called it removing "the first line of defense." The administration disputed the connection.8

"As the screwworm got pushed further south, there became less of a need to maintain the sterile fly facilities, so they were shut down."— reported in The Hill, June 2026

References & Citations

  1. USDA / APHIS — "New World Screwworm Outbreak in Central America and Mexico," aphis.usda.gov, 2025–2026.
  2. The Wildlife Society — "Another screwworm incursion inevitable, experts warn," wildlife.org, 2025.
  3. Drovers — "New World Screwworm in the U.S.: From Eradication to Resurgence," drovers.com, 2026.
  4. USDA — "USDA Announces Sweeping Plans to Protect the U.S. from New World Screwworm," usda.gov, Aug 15, 2025.
  5. USDA — "Secretary Rollins Suspends Live Animal Imports Along Southern Border," usda.gov, May 11, 2025.
  6. Investigate Midwest — "New screwworm threat halts cattle imports from Mexico," investigatemidwest.org, May 21, 2025.
  7. USDA / APHIS — "USDA Confirms Presence of New World Screwworm in the United States," aphis.usda.gov, June 3, 2026.
  8. The Hill — "Screwworm spread tests US readiness after staffing cuts," thehill.com, June 2026.

As Covered Elsewhere

USDA / APHIS USDA confirms the first U.S. screwworm case since the 1960s. Read → The Hill Spread tests U.S. readiness after agency staffing cuts. Read → Drovers From eradication to resurgence: how the barrier came down. Read →