Ticks are arthropods of the Ixodida order and belong to the Arachnida class, which includes also spiders, mites and scorpions. They are external parasites, and their size can range from a few millimetres to about 1 centimetre, depending on the species and development stage. They are characterized by a rounded body, indistinguishable from the head, and mouthparts (rostrum) that can pierce the skin of their hosts and suck their blood.