Blowfly strike (myiasis) caused primarily by the green bottle fly Lucilia sericata is one of the most serious welfare emergencies in sheep farming. Fly larvae feeding on living tissue cause intense suffering and rapid deterioration that can lead to death within days if untreated. Prevention and rapid response are essential components of responsible sheep welfare management.
Blowflies are attracted to warm, moist conditions and the smell of faeces, urine, or decaying tissue. Predisposing factors include dag (damp, faeces-contaminated wool), fleece rot, skin wounds, pizzle rot, and foot rot lesions. Flies lay eggs in affected areas; hatching larvae penetrate skin and feed on living tissue, releasing toxins and creating expanding wounds. Strike can progress from early-stage (fly activity, agitation) to severe (extensive tissue destruction) within 24-48 hours.
Early recognition is crucial for welfare and treatment success. Signs include: affected sheep separating from the flock, biting or kicking at their back end, stamping, tail wagging, and dark staining of fleece. Careful examination may reveal blue-green wool discolouration from fly activity, maggots, and characteristic smell. By the time obvious welfare signs are apparent, significant tissue damage may have occurred.
Treatment requires immediate clipping of affected wool, removal of all maggots (including larvae that have migrated from the primary site), wound cleaning, and application of appropriate wound care products. Insecticidal products licensed for blowfly treatment should be applied. Pain relief (NSAIDs) should be provided to improve welfare—struck sheep are in significant pain. Severe cases may require veterinary attention and systemic antibiotics. Early treatment dramatically improves survival and recovery.
Preventive measures include: dagging (removing damp, soiled wool from breech and tail areas), crutching (shearing around the breech), tail docking (though this itself raises welfare questions), management of predisposing conditions (foot rot, fleece rot), and strategic use of preventive insecticidal treatments (spot-on products, injectable preparations). Climate and fly risk should guide the timing of preventive treatments.
Regular flock inspection (at least twice weekly during peak fly season, daily during high-risk periods) is essential for early detection. Fly traps and meteorological fly-risk models can help predict high-risk periods and time preventive interventions. Electronic monitoring systems are being developed to detect behavioural changes associated with early strike.
Allowing sheep to suffer from untreated blowfly strike may constitute a welfare offence under animal welfare legislation. Farmers have a duty of care to inspect their flock regularly and provide prompt treatment. Farm assurance schemes typically include blowfly strike prevention and monitoring requirements as conditions of certification.