During the spring and summer months when populations of cattle lice normally decline, populations of the cattle biting louse (Bovicola bovis (L.)) built up repeatedly on stanchioned cattle but dropped decidedly on those not confined. Under the conditions of these tests, self-rubbing, meteorological conditions, and host metabolism appeared to have negligible effects on population fluctuations. It was concluded, therefore, that selflicking is an important mechanism by which cattle are able to protect themselves from lice.