Tick

Ticks are parasitic arachnids of the order Ixodida within the mite superorder Parasitiformes, typically three to five millimetres long, though they grow much larger once engorged with blood. They feed externally on the blood of mammals, birds and sometimes reptiles and amphibians, locating hosts by sensing odor, body heat, moisture or vibration, and the earliest known tick fossils date back roughly 100 million years to the Cretaceous period. The order divides into two main families, Ixodidae, the hard ticks, and Argasidae, the soft ticks, along with a third family, Nuttalliellidae, containing a single living species found in southern Africa; as blood feeders, ticks transmit numerous serious diseases to humans and animals.