Ticks are parasitic arachnids that are part of the superorder Parasitiformes. Along with mites, they constitute the subclass Acari. Adult ticks are approximately 3 to 5 mm in length depending on age, sex, species, and "fullness". Ticks are external parasites, living by feeding on the blood of mammals, birds, and sometimes reptiles and amphibians. It is estimated ticks originated during the Late Cretaceous period, approximately 120 MYA, the earliest tick fossil in New Jersey amber is dated at 90-94 million years old. Ticks are widely distributed around the world, especially in warm, humid climates.
