As a group, ticks are placed along with insects, spiders and mites in a large assemblage of organisms known as arthropods.
All arthropods have several pairs of jointed legs and a hard outside covering, or exoskeleton.
Ticks differ from insects in not having wings or antennae, and in having four, rather than three pairs of legs in most stages of their life cycle. About 800 species of ticks are known from throughout the world. All species are parasites in that they must locate, attach to, and feed from an animal in each stage of their life cycle. It is this life style, the feeding on blood from animals, that makes ticks of importance to human health. Ticks may transmit several diseases to people and domestic animals.