Cattle lice are among the most important arthropod (insect and mite) pests affecting dairy cattle in New York State and elsewhere in the United States. Lengthy, cool winters are particularly favorable to populations of lice, which thrive on animal skin that is protected by the long, winter-hair coat. Unlike fly pests, which feed on a variety of livestock and engage in many behaviors off the animals, lice are very host-specific and can survive for only very short periods of time off the host animal. Management of lice populations below economically injurious levels requires systematic monitoring and identification of these pests.