Black-tailed fawn with “hair loss syndrome” caused by the exotic lice Damalinia (Cervicola) sp.

Hair loss syndrome (HLS) of black-tailed deer is caused by a heavy infestation of Eurasian lice first reported in Western Washington in 1995.

When black-tailed deer become infested, they tend to develop a hypersensitivity (severe allergic) reaction, which causes skin irritation and excessive grooming by the deer. Eventually, this excessive grooming leads to loss of the guard hairs, leaving yellow or white patches along the sides.

Infestations are heaviest during late winter and early spring. The geographical distribution of HLS has expanded steadily since its first appearance and now affects black-tailed deer throughout their range in Western Washington and western Oregon. 

The exotic lice species described above does not affect humans or domestic animals.