Ticks and mites form the order Acari, a huge, diverse group of about 300 families and 30,000 species. They are found in every habitat, including aquatic ones, and have a wide range of lifestyles. Many are significant pests of crops and stored produce or parasitize humans and other animals. Most species are less than 1/32 in. long, although ticks can be much larger, especially following a blood meal. The body has no distinctive divisions, and the short abdomen has no segments. The mouthparts are carried on a special extension. The chelicerae are two or three segmented pincers or are adapted for piercing and sucking. Both the adults and nymphs have four pairs of six-segmented walking legs, although the first-stage larvae have only three pairs.
 

These flat ticks have a very tough, sometimes patterned plate on their back. In males, it covers the whole body; in females and immature ticks, it covers only the front half. The soft, flexible abdomen allows large blood meals to be taken from the animal hosts on which these ticks are found. Coloring varies from yellow to red or black to brown. Some species are highly marked.
 

After mating, a female gorges herself on blood and then drops off the host to lay a batch of eggs among vegetation. Six-legged larvae emerge, crawl up grass blades, and attach themselves to a passing host. A larva feeds for a few days and then drops off the host to molt into an eight-legged nymph. The nymph attaches itself to a host and feeds for several days before once again dropping off to molt into an adult.
 

Worldwide. In association with bird, mammal, and some reptile hosts.
 

Many deer ticks transmit disease and are serious pests of domestic animals such as cattle, sheep, horses, and poultry. Some also carry viral diseases that affect humans, including encephalitis, Lyme disease, tick typhus, and Rocky Mountain Spotted Fever.