For this presentation, we heard from Dr. Joan Burke, a Research Animal Scientist with the USDA. Her presentation covered the potential implications of New World Screwworm, and what it would mean if it were to become established here in the U.S. Following Dr. Burke’s presentation, Dr. Andrew Weaver shared additional context for solar grazing.

NWS is an infestation caused by the New World Screwworm fly laying eggs in the open wounds of warm blooded animals and can significantly impact livestock. Hatching larvae feed on animal tissue and can cause disease and tissue destruction. NWS was eradicated in the U.S. in the 1960s and mainly confined to South America since then. However, after NWS was detected in Mexico in late 2024, the U.S. restricted the live import of cattle, bison, and horses from Mexico in May of this year.

Dr. Burke began her presentation by discussing why New World Screwworm (NWS) is a concern and how it’s a significant threat to livestock operations. NWS has a devastating impact and high mortality rate, making it an economic threat for the US livestock industry. While it was previously eradicated from the US in 1966, it was recently detected in Mexico approximately 370 miles from the US sourthern border.

Dr. Burke described the distinct characteristics of NWS that differentiate it from common flies. NWS specifically seeks live animal tissue, causing progressive damage. Female flies lay 200-300 eggs at wound edges, leading to rapid reproduction. Larvae are pale-colored with encircling bands of dark spines, tapered at both ends. Adult flies have orange eyes and metallic blue/green bodies with three dark stripes.

After discussing the characteristics and concern of NWS, Dr. Burke discussed which animals and operations are most vulnerable. Newborn animals and sheep with open wounds are at heightened risk. Large flocks have a higher susceptibility due to challenges in thorough inspection. NWS thrives in warm, humid conditions, putting souther operations at risk.

Strategic efforts are underway to prevent NWS establishment in the U.S. The USDA is conducting surveillance along the southern border and suspending imports as needed. Research is also being done on a sterile fly program and trap deployment.

Dr. Burke and Dr. Weaver covered how solar graziers should respond and implement preventive measures. Sheep should be examined frequently, and any wounds should be promptly treated. Biosecurity and quarantine practices should be followed. Graziers should schedule high-risk procedures during cooler months and have an established veterinary0client-patient relationship before an emergency occurs.

Our speakers covered when to take action, as immediate response is critical for effective management. Graziers should contact their veterinarian immediately if any maggots are observed in any wound. If animals are affected, do not move them, but have veterinarians come to the site. If larvae are found, collect samples in 70% alcohol for laboratory identification. Prepare contingency plans for feeding and managing sheep if movement restrictions are imposed.

Dr. Weaver covered the unique challenges for solar graziers if NWS becomes established. The inability to relocate flocks between solar sites could severely impact contracts, and most solar sites lack the infrastructure needed for extended holding periods. Meeting vegetation management obligations during a quarantine period may be difficult, and confined sheep could cause overgrazing in quarantined areas. Additionally, solar operations have higher visibility than home farms, and could draw increased scrutiny.

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NWS Resources:

• ASI’s resources: https://www.sheepusa.org/education-resources/animal-health/new-world-screwworrm-resources
• Secure Sheep and Wool Supply: https://securesheepwool.org/
• Texas A&M’s resources:  https://agrilifeextension.tamu.edu/new-world-screwworm
• USDA, APHIS: https://www.aphis.usda.gov/livestock-poultry-disease/cattle/ticks/screwworm
• USDA NWS Webinar: https://www.youtube.com/watch?v=0ZdBU0mBXKE
• Questions: VS-Screwworm@usda.gov