Lethal Screwworm Fly Resurges in US Cattle 60 Years After Eradication, USDA Confirms

The Quick Take

• USDA confirmed two screwworm fly (Cochliomyia hominivorax) cases in Texas cattle, marking the pest's return after 60 years of eradication
• The two cases in Zavala County, Texas are geographically proximate, raising concern about a potential local breeding population
• The screwworm's return triggers concern for US-Mexico cattle trade protocols and could affect Americas beef supply chains

The US Department of Agriculture confirmed two cases of the screwworm fly — Cochliomyia hominivorax — in Texas cattle during the first week of June 2026, marking the pest's return to US soil 60 years after it was successfully eradicated through a decades-long sterile male release program. The two cases, found in young calves in Zavala County, Texas and a nearby area approximately 9 kilometers away, are geographically proximate, raising concern that the source is not an isolated import but a potential local breeding population. The screwworm is classified as one of the most destructive livestock pests globally because its larvae feed on living tissue of warm-blooded hosts.

The economic implications for US cattle producers and the beef supply chain are potentially significant. If the outbreak is not rapidly contained, the US could face import restrictions from major beef-importing nations that prohibit screwworm-affected cattle. Mexico and Canada, key US beef trade partners, have standing protocols to restrict cattle movement across borders if screwworm is confirmed at scale. Brazil and Argentina, as competing beef exporters, would be direct beneficiaries if US cattle production faces biosecurity restrictions. Livestock insurance companies with US agricultural exposure would also see claims risk rise, and cattle futures could reprice to reflect supply uncertainty.

The critical forward signal is the USDA's response protocol: if the agency deploys sterile male release at scale in Zavala County within days, the outbreak may be contained. Watch for any US state-level cattle movement restrictions or USDA trade advisories to major beef import partners. The macro variable is whether this remains a localized Texas event or spreads to neighboring states — the latter scenario would have outsized impact on cattle futures and beef inflation. Monitor CME Group's live cattle and feeder cattle futures for market pricing of this new biosecurity risk in US beef production.

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