Tick

Tick, name for a group of parasitic arthropods (order Acarina). Unlike most other arthropods, ticks have no head, and the thorax and abdomen are fused. All ticks are bloodsucking external parasites of vertebrates. They are divided into two main families: the soft ticks, Argasidae, and hard ticks, Ixodidae. Ticks transmit more diseases to humans and domestic animals than does any other arthropod group except the mosquitoes.