What are ticks?

If you want to remove one, see Tick removal

Ticks are small, blood-sucking arthropods related to spiders, mites and scorpions. There are many different species of tick living in Britain, each preferring to feed on the blood of different animal hosts. If given the opportunity, some of them will feed on human blood too. The one most likely to bite humans in Britain is the Sheep tick, Ixodes ricinus. Despite its name, the sheep tick will feed from a wide variety of mammals and birds. Bites from other ticks are possible, including from the Hedgehog tick, Ixodes hexagonus, and the Fox or Badger tick, Ixodes canisuga.

In the USA the highest risk comes from the Deer tick, Ixodes scapularis.

There are four stages to a tick’s life-cycle: egg, larva, nymph, and adult. Larvae, nymphs and adults all only feed once in each stage. The whole life cycle lasts around 2 years.

To the naked eye the larvae (with 6 legs) look like specks of soot, while nymphs are slightly larger, pinhead or poppy seed size. With their eight legs, nymphs and adult ticks resemble small spiders. It is the nymph which is most likely to bite you.

To see what an adult tick looks like in motion, watch this brief video. Public Health England have produced a longer 3 minute video with some very good images of ticks.


Where can they be found?

“I. ricinus is sensitive to climatic conditions, requiring a relative humidity of at least 80% to survive during its off-host periods, and is therefore restricted to areas of moderate to high rainfall with vegetation that retains a high humidity (i.e. litter layer and soil remain humid during the day). Typical habitats vary across Europe, but typically include deciduous and coniferous woodland, heathland, moorland, rough pasture, forests and urban parks.”[1]

Ticks can also sometimes be found in gardens, especially those with deep vegetation and a strong local wildlife population.

Numbers vary in different parts of the country and on a local basis, but ticks can be found across the UK [2]. Not all ticks carry disease, and infection rates in any one place may fluctuate from year to year.[3]

The risk may be higher in publicised areas such as the New Forest, but it is possible to be infected with Lyme disease anywhere in the UK: countryside, suburbia or town.

See Dr Sarah Randolph’s 2008 presentation How does tick ecology determine risk?

How do they pass on disease?

Ticks feed on the blood of other animals. If a larval tick picks up an infection from a small animal such as a vole, when it next feeds as a nymph it can pass the infection to the next animal or human it bites.

They cannot jump or fly, but when ready for a meal will climb a nearby piece of vegetation and wait for a passing animal or human to catch their hooked front legs. This behaviour is known as questing. The tick will not necessarily bite immediately, but will often spend some time finding a suitable site on the skin.

Once a tick has started to feed, its body will become filled with blood. Adult females can swell to many times their original size. As their blood sacs fill they generally become lighter in colour and can reach the size of a small pea, generally grey in colour. Larvae, nymphs and adult males do not swell as much as they feed, so the size of the tick is not a reliable guide to the risk of infection. If undisturbed, a tick will feed for around 5 to 7 days before letting go and dropping off.

The bite is usually painless and most people will only know they have been bitten if they happen to see a feeding tick attached to them.

The risk of infection increases the longer the tick is attached, but can happen at any time during feeding. A Public Health England leaflet for GPs points out that disease transmission can be in less than a day. As tick bites are often unnoticed, it may be difficult to determine how long it has been attached. Any tick bite should be considered as posing a risk of infection.

Adults are most often bitten around the legs. Small children are generally bitten above the waist—check their hairline and scalp.

See our detailed leaflet on ticks, “Ticks in Britain.”  (PDF 223KB)

The Public Health England website has some useful pages on ticks including a video and details of their tick recording scheme.

What diseases do ticks carry?

There are several diseases that can be caught from a tick bite in Britain. Three examples are

  • Lyme borreliosis [bore-EL-ee-OH-sis]
  • Babesiosis [bab-EE-see-OH-sis]
  • Ehrlichiosis [air-LICK-ee-OH-sis]

Globally, the list of diseases carried by ticks is much longer.

Some ticks carry more than one disease at the same time and can transfer them to you in a single bite. The resulting symptoms can be extremely confusing and liable to misdiagnosis. Treatment in such cases can be difficult. It is not known how often this happens in the UK.

See our leaflet on these diseases, “Tick-borne Diseases in Britain” (PDF 255KB)

How big are they?


The tick that generally bites humans (the nymph stage) can be as small as a poppy seed or full stop on this page.









1. Medlock et al. “Driving forces for changes in geographical
distribution of Ixodes ricinus ticks in Europe”. Parasites & Vectors 2013, 6:1


3. Bettridge et al. “Distribution of Borrelia burgdorferi sensu lato in Ixodes ricinus Populations Across Central Britain”. Vector borne and zoonotic diseases. 2013 Feb 19;13(X)