Tick, common name for members of a group of large mitelike arachnids parasitic on mammals, birds, and reptiles. All ticks are bloodsucking parasites. Ticks are found in most parts of the world but are generally limited to those habitats frequented by their hosts—namely, woods, tall grass, and shrubby vegetation—where they climb onto plants and wait to jump on a passing host.

Behaviour: Ticks spend a great deal of time waiting for their hosts. They are particularly sensitive to carbon dioxide and movement—signals that a host is nearby. Their grasping forelegs allow them to climb on a host. They quickly find a protected spot on the host’s body, sink their mouthparts into the flesh, and begin to feed. When full, they drop off the host. In some species, adult males and some nymph stages do not feed.

Importance: Several diseases are transmitted to humans and domestic animals through tick bites or tick excrement. The most important of these are spotted fever, relapsing fever, Lyme disease, tularemia, some forms of encephalitis, and Texas cattle fever (see Rickettsia). Usually, a particular tick-and-host combination harbors a specific disease organism, and often an infestation is limited to a relatively small geographical area.

“Tick,” Microsoft® Encarta® Online Encyclopedia 2009
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