Castor Bean Tick / Sheep Tick

Overview

Ixodes ricinus is the most common and most medically important tick in the UK. It bites humans, livestock, pets, birds, and wild mammals. It is the main vector for Lyme disease in Britain and also transmits several other pathogens.

You may see it called the "castor bean tick" (the engorged female resembles a castor bean) or the "sheep tick" (it is frequently found on sheep and deer).

Identification

• Adults: ~3–4 mm when unfed. Females have a dark-brown scutum (shield) on the front third of the body, with a pale grey abdomen that swells dramatically when engorged (up to ~11 mm). Males are smaller and entirely covered by a dark scutum.
• Nymphs: ~1–2 mm, about the size of a poppy seed. Pale brown, eight legs. This is the stage most likely to bite humans.
• Larvae: < 1 mm, six legs, very difficult to see with the naked eye.

Distribution in the UK

Found across all parts of the UK, particularly in woodland, heathland, moorland, rough pasture, and areas with bracken or long grass. Populations are densest in western and northern regions (Scotland, Wales, south-west England) where humidity is higher, but this species has been expanding its range and is now recorded in urban parks, gardens, and coastal paths.

Use our dashboard to check GBIF occurrence records near your postcode.

Life Cycle & Behaviour

The full life cycle (egg → larva → nymph → adult) takes 2–6 years depending on climate and host availability. Each active stage needs a blood meal from a different host before moulting to the next stage.

Ticks don’t jump or fly. They “quest” by climbing onto low vegetation and waiting with outstretched front legs for a passing host. They are most active when the temperature is above 4 °C and humidity is high, typically March–October.

Diseases & Public Health

Ixodes ricinus is the UK’s primary vector for:

• Lyme disease (Borrelia burgdorferi sensu lato) — the most common tick-borne infection in the UK, with around 1,000 laboratory-confirmed cases reported annually in England and Wales (the true number of infections is likely higher).
• Anaplasmosis (Anaplasma phagocytophilum) — uncommon in humans but circulates in livestock and wildlife.
• Babesiosis (Babesia spp.) — very rare in UK humans.
• Tick-borne encephalitis (TBEV) — the virus has been detected in ticks in parts of England; confirmed human cases remain extremely rare.
• Rickettsial infections — Rickettsia helvetica and others detected in UK ticks.
• Borrelia miyamotoi — a relapsing-fever spirochete found in Ixodes ticks across Europe.

Prevention & Advice

• Follow our bite prevention guide when visiting tick habitats.
• Check your body (and pets) after outdoor activity... remove ticks promptly.
• Monitor the bite site for up to 4 weeks. See your GP if a rash or flu-like symptoms develop — early treatment for Lyme disease is highly effective.

References & Further Reading

• NHS — Lyme Disease
• NHS Inform — Tick Bite Guide
• Lyme Disease Action — About Ticks
• UKHSA Tick Dashboard
• GBIF — Ixodes ricinus species page