What a tick is and what it looks like

Ticks are tiny parasites which feed on the blood of birds, reptiles and mammals (pets, farm and wild animals) including human beings.

Ticks vary in size (between 1mm to 1 cm), depending on lifecycle stage, gender, species and whether they have fed recently. Adult and nymphs have 8 legs, whilst larvae have 6 legs

• Ticks are bloodsucking, nonpermanent ectoparasitic (living on the skin of hosts) arthropods (no internal skeleton) that feed on mammals, birds, reptiles, and amphibians (1).
• Ticks are classified in the class Arachnida, subclass Acari (together with mites (2)), order Parasitiformes, and suborder Ixodida (3).
• Ticks have 4 stages to their life cycle: eggs, larvae, nymphs, adults.
• A distinguishing feature between the arachnids and insects is the presence of four pairs of legs in adult arachnids compared to three pairs of legs in insects (2). However, although adult ticks have four pairs of legs, the larvae (small immature form) have only three pairs of legs.
• Globally, there  are about 900 different species of ticks, most of which belong to one of the two main large families, the Argasidae (known as ‘soft ticks’) and the Ixodidae (known as ‘hard ticks’) (4).
• The structure of a tick consists of two parts – the capitulum, where the mouthparts of the tick are found (a distinct head is absent) and the body to which the legs are attached. Larval ticks have six legs, while nymphs and adults have eight legs (5). Ticks are visible to the naked eye but their size  varies according to the species, the lifecycle stage  of the tick and if the tick is fed or unfed. Unfed adult ticks range in length from 2 mm to 20 mm, depending on the species. Blood-engorged females may be 25 to 30 mm in length and weigh up to 100 times their pre-engorgement weight (5).
• As an example the nymphs of the tick Ixodes ricinus – the main vector of Lyme disease in the Northern Hemisphere - are 2 mm, unfed adult ticks are 2.4 - 3.6 mm and engorged females can reach up to 11 mm. More information about tick size can be found by visiting: http://www.bigtickproject.co.uk/

Dorsal view of Ixodes ricinus adult female	Ventral view of Ixodes ricinus adult female
Photo Credit: Nijhof AM. A contribution to the development of anti-tick vaccines. PhD thesis Utrecht University, the Netherlands. 2010. 216 p. https://dspace.library.uu.nl/bitstream/1874/179135/2/nijhof.pdf

Photo Credit: Prof. Lucy Gilbert From smallest (left) to largest (right) : Larvae; Nymphs; Adult Female. (Adult male not represented)