Tick is the common name for the small arachnids that, along with mites, constitute the order Acarina. Ticks are ectoparasites (external parasites), living by hematophagy on the blood of mammals, birds, and occasionally reptiles and amphibians. Ticks are second only to mosquitoes as vectors of human disease, both infectious and toxic. The major families of tick include the Ixodidae or hard ticks, which have thick outer shells made of chitin, and Argasidae or soft ticks, which have a membraneous outer surface. Ticks are blood-sucking parasites that are often found in tall grass, where they will rest themselves at the tip of a blade so as to attach themselves to a passing animal. It is a common misconception that the tick can jump from the plant onto the host. Physical contact is the only method of transportation for ticks. They will generally drop off of the animal when full, but this may take several days. Ticks have a harpoon-like structure in their mouth area, known as a hypostome, that allows them to anchor themselves firmly in place while sucking blood.