Flystrike (blowfly strike) is a severe and painful condition where blowfly larvae burrow into sheep flesh, causing rapid tissue destruction and death if not detected and treated promptly.
Blowfly strike causes some of the most extreme acute suffering seen in farmed sheep. The tissue destruction is rapid and extensive; affected sheep show behavioral signs of severe pain including isolation, teeth grinding, and skin trembling. Detection requires daily inspection during the fly season — a management burden that is often not met in extensive systems with large flocks. Prevention through chemical treatment, crutching (removing wool around the breech), and genetic selection for low-fold Merinos is highly effective. The ethical debate around mulesing centers on weighing the acute pain of the procedure against the chronic and potentially fatal suffering of repeated flystrike — alternatives including pain relief during mulesing and genetic selection for plain-bodied sheep are increasingly available.