Blowfly strike (cutaneous myiasis) is one of the most serious welfare emergencies in sheep—painful, rapidly progressive, and potentially fatal. Prevention and early detection are the foundations of welfare management.
Greenbottle flies (Lucilia sericata) are the primary cause of blowfly strike in Britain. Female flies lay eggs on soiled or moist fleece, wounds, or around the perineum. Larvae hatch within 12-24 hours and begin feeding on skin tissue, releasing proteolytic enzymes that liquefy flesh. Within 48-72 hours, untreated strike causes large tissue wounds, secondary bacterial infection, systemic toxaemia, and death. The pain from larvae feeding on living tissue is extreme.
Risk factors for blowfly strike include: warm, humid weather; soiled fleece from diarrhoea (scour); foot rot discharge; skin wounds; daggy or moist areas around the perineum; and dense fleeces that retain moisture. Prevention involves: regular dagging (removing soiled wool around hindquarters); treatment of conditions causing soiling; preventive insecticide application (organophosphate dips, synthetic pyrethroid pour-ons, insect growth regulators); and daily flock observation during risk periods (April-September).
Early strike signs include: restlessness, stamping, biting or scratching the affected area, and wool discolouration (dark, wet patch). Advanced strike shows large, maggot-filled wounds with characteristic smell. Treatment requires immediate removal of maggots (careful clipping and manual removal), wound irrigation, application of wound treatments, systemic antibiotics for secondary infection, and systemic NSAIDs for pain relief. Prompt treatment prevents progression from welfare-significant to potentially fatal.
RSPCA Assured and other welfare certification schemes require documented blowfly strike prevention programmes, regular flock observation, and specified response protocols. Farms with high blowfly strike prevalence are identified as requiring improvement actions. The welfare costs of blowfly strike are sufficiently severe that zero tolerance for preventable cases is an appropriate welfare standard—the tools for effective prevention are available and affordable.