Screwworm Fly Infestation Detected in US, Threatening Cattle Industry

On June 3, 2026, USDA veterinarians confirmed what livestock producers across the American Southwest had been dreading for over a year: the New World screwworm — a parasitic fly whose larvae feed on the living tissue of warm-blooded animals — had arrived in the United States. The host was a three-week-old calf in La Pryor, a small ranching community in Zavala County, Texas. Larvae were found burrowed into the animal's umbilical area [1]. Two days later, a second case was confirmed in another calf 5.6 miles away [2].

These are the first confirmed screwworm cases in U.S. livestock since 1966, when the country declared victory over a pest that once caused an estimated 230,000 livestock infections per year in Texas alone [3]. That six-decade gap was not luck — it was maintained by an elaborate international biosecurity system that, by multiple accounts, was allowed to deteriorate before this outbreak.

The Northward March

The current crisis traces back to 2023, when annual screwworm detections in Panama spiked from roughly 25 to over 6,500 cases, overwhelming the Darien Gap biological barrier that had served as the last line of defense [4]. From there, the fly spread through Costa Rica, Nicaragua, Honduras, Guatemala, Belize, and El Salvador. By mid-2025, it had reached southern Mexican states including Chiapas, Oaxaca, and Veracruz [5]. In April 2026, cases were confirmed in Nuevo Leon, Mexico — approximately 62 miles south of the U.S. border [6].

Source: USDA APHIS / National Reports

Data as of Jun 6, 2026CSV

As of early May 2026, Mexico had 1,717 active screwworm cases: 913 in cattle, 455 in dogs, 136 in swine, and 88 in horses [5]. The human toll across Central America and Mexico has reached over 1,190 infections and seven deaths as of January 2026, with 24 hospitalizations in Mexico [7]. The CDC confirmed the first U.S. human case — travel-associated, in a Maryland resident returning from El Salvador — in August 2025 [8].

A $850 Million Emergency Response

The federal response has been substantial but reactive. Within 24 hours of the first Texas confirmation, USDA launched aerial releases of two million sterile screwworm flies twice weekly over the detection zone, supplemented by four million additional sterile flies per week deployed through 24 ground release chambers [1]. Governor Greg Abbott declared a state disaster for all Texas counties on June 5, authorizing all available state resources [9].

The broader containment strategy carries an $850 million price tag. The centerpiece is a $750 million sterile fly production facility at Moore Air Force Base in Edinburg, Texas, being built with the Army Corps of Engineers and designed to produce up to 300 million sterile flies per week [10]. Construction is expected to take at least a year, with an operational target of November 2027. In the interim, USDA committed $100 million in temporary acceleration funding and $21 million to retrofit a fruit fly facility in Metapa, Mexico, to add 60 to 100 million sterile flies weekly [10].

The sterile insect technique (SIT) — which works by flooding an area with irradiated male flies that mate with wild females but produce no offspring — is the same method that eradicated the pest from North America between 1957 and 1966. That original campaign cost $32 million, or roughly $290 million in inflation-adjusted dollars [11].

Source: USDA / CRS Reports

Data as of Jun 6, 2026CSV

Agriculture Secretary Brooke Rollins stated that no infestations beyond the two Zavala County calves had been detected as of June 6 [2]. USDA Under Secretary Dudley Hoskins noted that models had predicted screwworm entry in 2025, but preparation efforts "bought time" before the June 2026 confirmation [1]. Additional measures include screwworm-sniffing dogs posted at U.S.-Mexico border crossings and expanded mounted border patrols [12].

The Biosecurity Breakdown

The question now being asked in Congress and across the agricultural sector is straightforward: how did a pest eradicated 60 years ago get back in?

The primary defense was COPEG, the U.S.-Panama Commission for the Eradication and Prevention of Screwworm, which operates a sterile fly production facility in Panama. USDA's Animal and Plant Health Inspection Service (APHIS) has historically funded 90% of COPEG's activities and estimated the investment saved the U.S. cattle industry $2.3 billion annually [13].

Multiple factors appear to have weakened this barrier simultaneously. APHIS lost 2,105 employees — 25% of its workforce — during the Department of Government Efficiency (DOGE) staffing reductions in 2025 [14]. In March 2025, the Trump administration terminated more than 100 U.S.-funded FAO programs valued at approximately $382 million, including projects that monitored and contained screwworm in Central America. The FAO's global health security program subsequently reduced its screwworm surveillance [15].

Critics argue that these cuts came at the worst possible time. "The cuts and subsequent emergency reinvestments show a pattern of defunding prevention, then spending far more on emergency response," one Congressional Research Service report noted [16]. USDA has not publicly released a detailed year-by-year budget history for COPEG or the broader buffer zone program, making independent verification of long-term funding trends difficult. What is documented is that the $850 million emergency response dwarfs what consistent annual maintenance of the barrier system would have cost.

Defenders of the administration's approach point to the $850 million commitment itself as evidence of seriousness, and note that the screwworm surge in Panama began in 2023 — before the staffing reductions. The explosive growth of cases in the Darien Gap also coincided with a surge in human migration through the region, which may have facilitated the movement of infected animals [17].

The Economic Stakes

The outbreak arrives at a particularly vulnerable moment for the U.S. beef market. The domestic cattle herd is at a multi-decade low. Annual cattle prices are forecast at $235.75 per hundredweight for 2026, and retail beef at $9 per pound is expected to become common [18]. Beef demand is at its highest level since 1983, while 2026 production has been forecast down by 243 million pounds to 25.547 billion pounds [18].

Source: BLS / Bureau of Labor Statistics

Data as of Apr 1, 2026CSV

Food prices are already elevated: the CPI for food stood at 348.5 in April 2026, up 3.2% year-over-year [19]. The broader Consumer Price Index hit 332.41 in the same month, up 3.8% annually [20].

The screwworm threat compounds existing supply pressures. The U.S. closed its border to live cattle imports from Mexico on May 11, 2025, shutting off a pipeline of roughly one million head annually — representing 5% of feedlot placements and up to 20,000 head per week during peak season [21]. Mexican cattle exports collapsed to $335 million in 2025, a 78.2% decline from the prior year [22]. Some Southwest feedlots are now facing closure due to tightened supply [21].

USDA estimated a screwworm outbreak in Texas alone could cost $1.8 billion in livestock deaths, labor, and medication [23]. A separate legislative study in Oklahoma, led by state Senator Casey Murdock, estimated an equivalent $1.8 billion cost for that state [24]. Treatment for an individual affected cow runs approximately $452 — a process involving the manual removal of hundreds of larvae and thorough wound disinfection [25].

David Anderson, a livestock economist at Texas A&M, summarized the industry sentiment: "This is a pest we don't want back. This is a bad thing" [26].

Tariff dynamics add another layer. While tariff adjustments in late 2025 may facilitate some beef imports, analysts have noted these are "unlikely to do much more than slightly mitigate ground beef prices" and will have "no impact on beef cut prices, such as steak" [27].

Insurance Gaps and Small Rancher Vulnerability

The federal Livestock Indemnity Program (LIP), administered by the Farm Service Agency, covers livestock deaths from adverse weather events or attacks by federally reintroduced or protected animals, paying 75% of average fair market value [28]. Ranchers must file notice of loss within 30 days and apply within 60 days after the end of the calendar year.

The critical gap: LIP does not explicitly cover pest or parasite losses like screwworm [28]. The Livestock Risk Protection (LRP) and Livestock Gross Margin (LGM) programs protect against price declines and margin compression, respectively, but neither addresses direct animal mortality from parasitic infestation [28].

This leaves ranchers exposed. Most U.S. cattle operations do not carry private insurance against pest-related livestock loss, and no federal indemnity program is currently structured to compensate for screwworm mortality. If containment fails and screwworm becomes established — or "enzootic" — in southern states, the long-term cost structure would fall disproportionately on smaller family operations. Industrial feedlots can absorb the per-head treatment costs, implement systematic surveillance protocols, and spread compliance expenses across larger herds. A family operation running a few hundred head faces the same $452-per-animal treatment cost with far less margin [25].

Mandatory treatment protocols, regular wound inspections during calving season, and ongoing surveillance would add labor costs that scale poorly for operations already running thin. Texas A&M AgriLife Extension has begun publishing guidance on "rethinking livestock management to consider screwworm," but the adjustment burden remains steep [29].

Wildlife at Risk

Screwworm does not distinguish between livestock and wildlife. The 2016 Florida Keys outbreak — the last time the fly appeared on U.S. soil — killed 135 Key deer, representing 9 to 20% of the total population of an endangered subspecies found only on islands from Little Pine Key to Sugarloaf Key [30]. Over 50 additional deer were in such poor condition they had to be euthanized. That outbreak was contained within seven months using SIT, but experts warned at the time that "another screwworm incursion [is] inevitable" [30].

White-tailed deer, which number in the tens of millions across the southern United States, are highly susceptible. So are feral hogs, whose large populations in Texas could serve as a reservoir making eradication more difficult. Conservation groups have raised concerns that the current eradication strategy prioritizes cattle over wildlife, though USDA's aerial sterile fly releases are geographically broad enough to benefit all warm-blooded species in the treatment zone [12].

The wildlife dimension also complicates containment. Unlike cattle, wild animals cannot be inspected, treated, or moved into quarantine. If screwworm establishes breeding populations in wildlife, eradication becomes significantly harder — a lesson from the Florida Keys, where the fly persisted in deer populations even as domestic animals were treated [30].

The 2016 Precedent and What It Tells Us

The Florida Keys outbreak offers both reassurance and warning. On one hand, the U.S. successfully eradicated screwworm from the Keys in under a year. On the other, that outbreak was geographically isolated on a small island chain with limited wildlife populations. The current situation in South Texas — contiguous with the Mexican border, surrounded by vast ranchlands, and home to large populations of deer and feral hogs — presents a fundamentally different challenge [4].

The sterile fly production infrastructure needed to fight this battle at scale does not yet exist on U.S. soil. The existing COPEG facility in Panama produces 100 million sterile flies per week [10], but those flies are needed to fight the ongoing Central American outbreak. The new Texas facility will not be operational until late 2027 at the earliest. In the interim, the U.S. is relying on temporary measures and the retrofitted Mexican facility.

What Happens If Containment Fails

If screwworm becomes established in the southern United States, the consequences would extend well beyond the immediate outbreak zone. Texas, with approximately 13 million cattle, Oklahoma with 5.2 million, and other Gulf Coast states would face mandatory inspection and treatment regimes. The 20 km quarantine zones currently in place around the Zavala County detections would need to be replicated across any area with confirmed cases [1].

The structural economics of American beef production would shift. Ranchers in affected areas would face recurring costs for wound treatment, preventive inspection during vulnerable periods like calving and branding, and compliance with surveillance mandates. These costs would be built into the price of beef permanently, not as a one-time shock but as a new baseline operating expense.

For consumers, the interaction of screwworm-related supply disruption with existing tariff pressures and a historically small cattle herd creates conditions for sustained beef price increases. The precise magnitude depends on the geographic scope of any established infestation, but the combination of factors — restricted Mexican imports, a shrinking domestic herd, rising demand, and now a parasitic threat — points in one direction.

Senator Murdock, himself a cattle rancher, framed the stakes plainly: "Agriculture is a major part of Oklahoma's economy, and we have to take this threat to animal safety very seriously" [24].

The next 12 to 18 months — the window before the new sterile fly facility becomes operational — will determine whether the United States can repeat its 1966 success or faces a long and expensive coexistence with a pest it thought it had defeated.