Ticks and mites are arthropods related to insects that may become numerous and damage horses in some years. Several species of ticks may occasionally become pests on horses in North Dakota. Dermacenter variabilis, the American dog tick, and Dermacenter albipictus, the winter tick (Figure 13), cause the most frequent problems. Both species are similar in appearance. Unfed stages are very flat and hard. Before ticks feed they are about 1/4 inch long. Ticks attach to the vertebrate host to obtain a blood meal; heavy populations may cause the death of animals from excessive blood loss. Engorged ticks are about 1/2 inch long and look inflated. The adults have eight legs. The engorged female tick drops from the host and lays large numbers of eggs (up to 6000) on the ground.

The winter tick is a one host tick; this means that all stages in the developmental cycle can parasitize the same type of host animal. The preferred host for the winter tick is the moose; however, horses are frequently fed upon. Occasionally cattle, sheep, bison and other large animals are attacked. The winter tick is most abundant during the fall through the winter months. Heavy infestations cause loss of appetite, depression and debilitation of horses.

The American dog tick is a three host tick. Larvae and nymphs feed on rodents and small mammals. Adult dog ticks feed on a variety of larger mammals including horses, cattle and humans. Grooming of horses should reveal ticks which are present.