Dreaded Screwworm Is Detected 60 Miles From Texas

A parasitic fly that can wipe out livestock has been detected uncomfortably close to the US–Mexico border, and Texas officials say the state is firmly "in the crosshairs." A calf in Nuevo León, Mexico, roughly 60 miles from South Texas, has tested positive for New World screwworm; it marks the northernmost active case in Mexico, Texas Agriculture Secretary Sid Miller said Monday. A case was previously reported in Nuevo León in September; prior to that, the closest case of New World screwworm in cattle had been one detected 370 miles from the US border.

Miller noted that the impacted calf is located "within the current sterile fly dispersal zone," where some 100 million sterilized screwworm flies are being released by the USDA each week, reports KFOR. That number will grow once a new $610 million facility at Moore Air Base near Edinburg, Texas, comes online. The Houston Chronicle reports the USDA and US Army Corps of Engineers broke ground on the building on Friday. The USDA expects to begin producing 100 million sterile flies a week there beginning in November 2027 and then scale up to 300 million weekly.

Screwworm flies lay eggs in open wounds, and their larvae feed on living flesh, making them a major risk to livestock. Border livestock imports from Mexico remain blocked, and Agriculture Secretary Brooke Rollins says Texas ports won't reopen until the parasite is pushed much farther south.