Lambs may be infested within 24 hours of birth. Transmission may occur by walking over contaminated pasture or by close contact with infested animals. One flock observed for two years showed that the lice population increased in the winter, occurring in greatest numbers on the face and neck of the sheep in spring. Infestations tended to spread down the front of the neck, with sparser populations scattered over the rest of the body. The face louse has been reported on the tail and on the scrotum of rams.
Affected areas have a reddish brown appearance.
The face louse appears more susceptible to cold than the foot louse and does not occur in clusters. The life cycle is about five weeks, similar to the biting louse. Treatment Information on treatment is limited. Eggs resist treatment, which therefore should be repeated 10 days after eggs have hatched to ensure total eradication. However, a second treatment may not be necessary if sufficient residual chemical remains to kill emerging nymphs.