What is a tick?

Ticks are small parasites, which feed on the blood of mammals (including humans), reptiles and birds. They are closely related to spiders and mites.

Ticks do not have wings to fly. They also cannot jump. They travel by walking on the ground and up plants.

Ticks locate a host (the person or animal they will feed on) by picking up chemical cues from breath and body odour, as well as heat, vibrations and shadows. They latch onto a passing or resting host by using special hooks on their legs.

Some species of tick live in the burrows or nests of animals and birds and complete their life cycle there.


Ticks vary in colour (ranging from reddish to dark brown or black), and differ in size, depending on the species, age and sex of the tick, and whether it has fed.

Tick sizes

Ticks are very tiny. Many people think of them as being quite big, but this is because they are used to seeing a balloon-like tick on a dog or cat. This is how the nymphs or adult ticks look after they have fed for several days and are full of blood. By this time, they look like a pink or blue-black balloon, and often protrude from the pet’s fur.

An unfed female is approximately 3mm (sesame-seed-size) and she is small, oval and flat. When fully engorged, she can reach 11mm. Unfed males are smaller, at approximately 2.5mm. Unfed nymphs (which are semi grown) are smaller still, at around 1.5mm, and the larvae (which are newly hatched) are a tiny 0.5mm (the size of a poppy seed). Even at such a tiny size, larvae can still transmit certain infections. Once fed, a tick can become considerably bigger, with the exception of the male, which takes smaller meals.

The tick’s life cycle

Like the rest of their ‘relations’, the spiders, scorpions, mites and harvestmen, ticks have eight legs. However, when they hatch from their eggs (at this stage, they are called ‘larvae’), they only have six legs. They immediately need to feed to gain strength and to grow and moult to their next stage (when they become nymphs).

At the nymph stage, they have eight legs. They continue to feed and moult to the last stage, which is an adult.

Ticks in the UK

There are two families of ticks that can be found in the United Kingdom:

1. Argasidae – which are a ‘soft tick’ family. They are called soft ticks because they have a spongy and wrinkled back, which extends like a hood over their mouth parts.

2. Ixodidae – which are a ‘hard tick’ family. They are called hard ticks because they have a hard plate-like shield that covers their backs. Unlike soft ticks, the mouth parts can be seen from above because the shield does not cover them.

As a hard tick feeds and swells up with blood, the shield on its back appears smaller and more towards its head.

There are many species of ticks in each of these families. It is usually a species of hard tick that is found on domestic pets or people, although some soft ticks will bite, given the opportunity.

What ticks are a risk to people and pets?

Three particular species of hard tick are more likely to attach to people and their pets in the UK. One is Ixodes ricinus (also known as the sheep tick, wood tick, deer tick and castor bean tick). The second is Ixodes hexagonus (also known as the hedgehog tick). The third is Dermacentor reticulatus (also known as the ornate cow tick or the marsh tick). However, there are over 20 species of ticks in Britain, and a number of them have been known to attach to people or pets. It can depend on the area, habitat and surrounding wildlife, as to which species are most abundant.

Ticks normally choose wildlife and farm livestock to be their hosts. However, people and pets send out the same signals (body heat and chemicals) as the tick’s usual hosts. The tick recognises these signals as being from a potential host and they will readily attach. Because we are not generally the intended host, we become ‘incidental hosts’, meaning that we are just in the wrong place at the wrong time.

Due to various factors, ticks are more abundant and are active for longer periods (even at low temperatures), therefore it has become more common for us to be incidental hosts.

Female sheep tick.

Male sheep tick.

Various tick sizes