Tick, coloured scanning electron micrograph (SEM). Ticks (superfamily Ixodoidea) are small arachnids. They are ectoparasites, feeding on the blood of mammals, birds, and occasionally reptiles and amphibians. They transmit several diseases, including Lyme disease, Colorado tick fever, relapsing fever, and a form of meningoencephalitis, along with other diseases. Magnification: x80 when printed 10 centimetres wide.