There are three factors that determine the risk of flystrike in the flock.

Susceptible sheep
The most important determinants of breech strike risk are breech wrinkle and dag (in high rainfall areas). Other factors that can increase the risk of breech strike include breech cover, yellow wool and urine stain.

The most important determinant of body strike is fleece rot. Other factors that can increase the risk of body strike include body wrinkle, lumpy wool, wool colour and structural conformation.

Flystrike can also occur in conjunction with pizzle stain, footrot, staining of wool with birth fluids, physical injury (eg. poll damage and marking wounds) and existing strike. For more information click here.

Female flies ready to lay eggs
More than 90% of strikes are caused by the green sheep blowfly, Lucilia cuprina.  In most sheep producing areas of Australia, Lucilia survives through winter as post-feeding larvae or pre-pupae in the soil, so flystrike is not generally a problem during this time - click here for more information. It is important to know when flies emerge from over-wintering in your area, as this is when the main flystrike risk period begins. For more information click here.

Weather conditions must be suitable
Warm and moist conditions favour both activity of blowflies and the development of predisposing conditions in sheep. These conditions occur most often in spring and autumn and during prolonged wet conditions during summer. If the weather is cool (less than 17ºC) or too windy (> 30 km/hour) sheep blowflies are usually not active. Very hot dry conditions in mid-summer also suppress fly activity and reduce sheep susceptibility. To read more, click here.