A Dutch survey showed myiasis occurring more frequently on farms with over 25 ewes compared to smaller farms. Occurrence was most frequently associated with hot and humid weather and was mainly observed in the area around the tail. Ewes and ewe lambs had significantly more myiasis than rams and ram lambs. There was no relationship with tail docking, breed time of shearing, soil type, the environment (bush, trees, water, etc.), type of treatment, the insecticides used, the number of preventive treatments, the time of treatment or the number of flock observations.