Screwworm Information
New World screwworm (NWS) is a serious pest of livestock and wildlife.
This invasive pest we previously eradicated from the United States, but has recently been reintroduced (June 2026). Website links below provide information on screwworm, including prevention and treatment for screwworm. Treatment and prevention, as well as reporting requirements, often vary by state - contact animal health officials in your state for state-specific requirements and recommendations.
FEDERAL RESOURCES
STATE RESOURCES
-
California Department of Food and Agriculture (CDFA)
-
University of California at Riverside
-
Florida Department of Agriculture & Consumer Services
-
Texas Animal Health Commission
-
Texas A&M Agrilife Extension
-
New Mexico State University
-
University of Tennessee
-
Univeristy of Arkansas
COMMODITY GROUP RESOURCES
-
AVMA
-
NCBA
-
Swine Health Information Center
-
American Sheep Industry Association
Face Fly
Face flies (Musca autumnalis) are pests of pastured livestock animals such as beef cattle, heifers, and horses. As adults, females use their sponging proboscis with teeth to feed and scrape at wounds and around moist-mucus membranes of an animal’s face. The pain from this feeding behavior makes livestock nervous, and they are forced to spend their growing days in shade avoiding feeding. While feeding face flies can also transmit pathogens such as Moraxella species and Brucella abortus which cause pink eye, bovine viral diarrhea virus, and Thelazia eye worms. These flies lay their distinctive eggs with a black respiratory stalk in fresh dung and then hatch into larvae which undergo three instars. During the final instar, the larva migrates from the dung to a drier area and pupates inside a white calcified puparia. Males emerge prior to females, and both sugar feed on flowering plants for nectar. These cosmopolitan flies are native to Europe and central Asia, but are now found throughout North America north of 35⁰N. Understanding their biology is key to management and control; thus, face flies are controlled in the immature stage using feed-through insecticides that prevent development (e.g., ivermectin) whereas adults are managed with repellents and insecticides (e.g., permethrin-based products).





