Screwworm Cases Surge Across Southwest: What It Means and How to Respond

USDA is maintaining a 24/7 response to New World screwworm (NWS) as activity increases in parts of the Southwest. USDA Undersecretary for Marketing and Regulatory Programs Dudley Hoskins cites warm, wet conditions in New Mexico and Arizona as one factor supporting the fly population and stresses continued surveillance, trapping and prompt reporting are central to the response.

“When you look at the environmental factors on the ground, especially in New Mexico and Arizona, the amount of rainfall and moisture that they have in those environments right now” and the temperatures have created favorable conditions, Hoskins explains. “Those two things, hot and wet, are things that the screwworm fly love.”

State agricultural leaders on the front lines agree. Dr. Bud Dinges, Texas Animal Health Commission (TAHC) executive director and Texas state veterinarian, says weather conditions are playing a direct role in recent detections.

“There are many factors that could play into the uptick in cases as of late. Namely, weather conditions are certainly a factor. Increased rainfall and moisture, combined with lower temperatures, are conducive for NWS activity,” Dinges explains. “West Texas is very green and wet, ideal NWS fly conditions.”

In Arizona, Department of Agriculture Director Paul Brierley echoes that assessment, pointing to abnormal precipitation that created lush forage across the desert landscape.

“I’m pretty sure that it’s the fact that we’ve had record rainfall and now new grass, and they love the warm, moist environment. So I’m pretty sure that’s what has done it,” Brierley says. “It’s all the Southwest states where it’s hitting, and we’ve had just record rain and flooding, and that leads to grass.”