Sheep Fly Strike (Blowfly Myiasis): Prevention and Welfare Response

Fly strike is a painful and rapidly fatal condition affecting sheep, caused by blowfly larvae feeding on living tissue. Prevention and rapid detection are critical welfare priorities.

Key Facts

Fly strike occurs when blowflies lay eggs on sheep, particularly in wet, soiled or dag-covered areas of the fleece
Larvae hatch within hours and begin feeding on the sheep's skin, creating progressive wounds
Untreated strike can kill a sheep within days through shock, toxaemia, and organ failure
Strike risk peaks in warm, humid weather between spring and autumn
Preventive treatments include insecticides applied to the fleece, mulesing (controversial), and dagging
Genetic selection for reduced breech wrinkle is a long-term welfare improvement strategy

Welfare Considerations

Fly strike causes extreme suffering. Affected sheep experience intense pain and distress from tissue destruction caused by feeding larvae. The rapid progression of the condition means brief periods of undetected strike can cause severe wounds. Welfare-centred fly strike management involves regular inspection (at least every 3 days during high-risk periods), prompt treatment on detection, appropriate preventive treatments, and dagging to remove soiled wool that attracts flies. The welfare cost of fly strike justifies preventive treatments including topical insecticides, despite their environmental concerns, as the alternative causes significant animal suffering.

What You Can Do

Inspect sheep at least every 3 days during warm weather — look for discolouration and odour in the fleece
Apply veterinary-approved preventive treatments at appropriate times of year
Dag sheep regularly to remove soiled wool and reduce strike risk
Treat affected sheep immediately — delay significantly worsens outcomes
Select for sheep genetics with reduced breech wrinkle to reduce long-term strike susceptibility