Flystrike season is upon us now and we have seen quite a few struck sheep lately – mostly in cases whereby a preventative treatment has not been applied. While keeping an eye out for flies is useful, flystrike can occur very quickly over a couple of days, especially in ideal conditions, so we always recommend applying a preventative during the risk period. 

Blowflies thrive in conditions which are warm, humid and sheltered (with peaks seen from summer through to autumn). Flies are attracted by smell, especially wet fleece, faeces and urine (daggy sheep), cuts (eg. From shearing), bacterial or fungal infections, or foot-rot. In sheep, flies will commonly strike the crutch, back, legs and pizzle in males.

Flystrike not only damages and discolours the sheep’s wool; it also causes significant stress, leading to weight loss and wool loss. Severely struck sheep may suffer septicaemia (blood poisoning) and dehydration. These sheep can die if immediate action is not taken.

In New Zealand, there are two main categories of flies which can cause flystrike: primary strike flies and secondary strike flies. Primary strike flies can initiate strike on intact skin (ie. no open wounds are required), whereas secondary strike flies require a pre-existing wound, such as a shearing wound.

Flystrike infestation often occurs very quickly. Maggots hatch within 12-24 hours after the egg is laid. 3-7 days after the egg is laid, the maggots are fully grown. The maggot’s skin hardens to form pupae. 3 days to 4 weeks later an adult fly emerges. 2 days later, the fly is sexually mature and can begin laying eggs.

Signs of flystrike:

  • Behavioural signs (restless, shade-seeking, tail twitching, nibbling affected area, stamping feet)
  • Blackened fleece and/or loss of wool in patches
  • Sores on skin containing maggots or eggs


Preventing flystrike:

  • Crutching sheep and tailing lambs
  • Removing dags and keeping wool short (sheep should be shorn yearly)
  • Drench check sheep that are daggy or have loose faeces (faecal egg count at the vets)
  • Get a vet to check sores, wounds and foot problems
  • Remove dead animals from farm which may attract flies
  • Apply fly preventative product – give us a call to discuss or dispense products for your sheep


If you think your sheep may have flystrike, give us a call so we can discuss treatment options.