Ticks: 
various ticks
Ixodidae - hard ticks
Argasidae - soft ticks
There are two well-established families of ticks, Ixodidae (hard ticks), & Argasidae (soft ticks). Both are important disease causing agents to human and animals. Ticks transmit the widest verity of pathogens of any blood sucking arthropod, including bacteria, protozoa, rickettsiae, & viruses. Tick-borne pathogens include ehrlichiosis, babesiosis, tularemia, tick-borne relapsing fever, Lyme disease, & Rocky Mountain spotted fever. Ticks from the family ixodid, in particular the l. scapularis species, play a huge role in transmitting Lyme disease
Ticks can be found worldwide but they tend to flourish in moist, humid environments because they need a certain amount of moisture in the air to undergo metamorphoses. 
Deer tick (l. scapularis)There are two critical requirements for tick survival: there must be enough humidity in the air for ticks to remain hydrated & there must be a high population of host species. It has been determined through geographical information systems (GIS) that sandy soil, rivers, hardwood trees, & the presence of deer are good predictors in supporting a dense tick population.
The body of a tick is separated into two primary sections the posterior containing the legs, reproductive organs, and digestive tract (idiosoma) and the anterior consisting of the head and mouthparts (capitulum or gnathosoma). The outside surface (cuticle) of a hard tick grows to accommodate the large volume of blood ingested.
Rocky Mountain wood tick (Dermacentor andersoni) Ticks satisfy all their nutritional requirements on a diet of blood (hematophagy). They extract blood by puncturing the host’s skin, and then inserting their hypostome (calcified structure near the mouth, maxilla), which secretes a cement-like substance, gluing the tick into place while feeding. This cement substance is produced in the salary glands and dissolves when feeding is complete. Hard ticks can feed on their host for several days to weeks depending on the tick species, host involved, & the life-stage of the tick.
Hard ticks seek host by, a behavior known as “questing”, perching themselves on the edges of leaves or branches and attaching themselves to a host that unexpectedly brushes up against them. Certain biochemical’s such as carbon dioxide, heat, and movement 
American dog tick ( Dermacentor variabilis)serve as stimuli for questing behavior.
Hard ticks are most commonly collected for research by the use of "flags" or "drags" which are made from 1 m square pieces of roughly textured fabric such as fleece or flannel attached to a rod handle. The flags are slowly dragged across the surface of vegetation to collect questing ticks.
Both ixodid and argasid ticks undergo three primary stages of development: larval, nymphal, and adult. Ixodid ticks require three hosts, and their life cycle takes at least one year to complete. Up to 3,000 eggs are laid on the ground by an adult female tick. When larvae emerge, they feed primarily on small mammals and birds. After feeding, they detach from their host and molt to nymphs on the ground, which then feed on larger hosts and molt to adults. Female adults attach to larger hosts, feed, and lay eggs, while males feed very little and occupy larger hosts primarily for mating.
Argasid ticks, unlike ixodid ticks, may go through several nymphal stages, requiring a meal of blood each time.
Actual size of tick Their lifecycle ranges from months to years. The adult female argasid tick can lay anywhere from a few hundred to over a thousand eggs over the course of her lifetime. Larvae feed very quickly and detach to molt to nymphs. Nymphs may go through as many as seven instars, each requiring a blood meal. Both male and female adults blood-feed, and they mate off the host. During feeding, any excess fluid is excreted by the coxal glands, a process which is unique to argasid ticks
Rash from Lyme diseaseThere are six known species of public health significance in California: 2 soft ticks, Ornithodoros hermsi and the Ornithodoros coriaceus (pajahuello tick), and four hard ticks, Dermacentor andersoni (Rocky Mountain wood tick), Dermacentor occidentalis (Pacific Coast tick), Dermacentor variabilis (American dog tick), and Ixodes pacificus (western black-legged tick). The adults of D. andersoni, D. variabilis and, the larvae, nymphs, & adults of, the D.occidentalis, bite people.
Here is a short movie about ticks
Ticks are most commonly encountered when visiting areas with heavy vegetation and brush. Parks, wilderness areas, and fields are common tick areas.