Sheep Fly Strike (Blowfly Myiasis): Welfare Emergency

Blowfly strike is one of the most painful and rapidly life-threatening conditions affecting sheep. Early detection and prevention are vital welfare priorities for sheep farmers worldwide.

Key Facts

Blowfly strike (myiasis) occurs when blowflies (primarily Lucilia sericata in the UK) lay eggs on sheep, usually in warm, damp, soiled wool; hatching maggots then feed on skin and tissue
The green bottle fly is most commonly responsible in the UK; Calliphora species and other blowflies cause strike in other regions
Strike can kill a sheep within days — maggots release ammonia and enzymes that digest skin, cause systemic toxaemia, and create open wounds highly attractive to secondary flies
Risk factors include dirty (dung-stained) fleece, wounds, footrot, and overgrown wool; warm, humid weather significantly increases fly activity
Prevention options include regular dagging (removing soiled wool), treatment with organophosphate or insect growth regulator-based products, and genetic selection for low-strike-risk wool characteristics
Mulesing — surgical removal of skin folds around the breech area — is practised in Australia to reduce strike risk; it is controversial due to the acute pain it causes and is being phased out in many markets
Strike often goes undetected for days because sheep may hide signs of discomfort — by the time visible distress or wool pulling is noticed, significant tissue damage has often occurred
In the UK, sheep not inspected regularly during blowfly season (April–October) can suffer severe welfare harm from undetected strike

Welfare Considerations

Blowfly strike causes intense, prolonged suffering. The sensation of hundreds or thousands of maggots feeding on living tissue, combined with the toxaemia from maggot secretions, creates extreme distress. Affected sheep may be found collapsed, disoriented, or in obvious pain — but because sheep mask vulnerability, early-stage strike is often subtle and easily missed. The welfare burden is compounded by the fact that the condition is almost entirely preventable with appropriate monitoring and preventive treatment. Delayed detection significantly worsens the welfare outcome and the prognosis for the animal. Immediate treatment involves removing maggots, clipping wool from the affected area, applying wound treatment, and assessing systemic effects — veterinary input is essential for severe cases.

What You Can Do

Inspect sheep daily during blowfly season (April–October in the UK), especially around the breech, shoulders, and any wounds
Apply preventive blowfly products at the start of the season and after shearing, following label instructions
Dag sheep regularly to remove soiled wool that attracts flies
If strike is detected, treat immediately — remove maggots, clip the area, and seek veterinary advice for severe or systemic cases
Report concerns about sheep welfare (undetected or untreated strike) to the RSPCA or equivalent animal welfare authority