Sheep tick. Coloured scanning electron micrograph (SEM) of the underside of a sheep tick (Ixodes ricinus). The ticks mouthparts (centre) are between its two front legs. This arachnid is the principal vector of Lyme disease, which is caused by the bacterium Borrelia burgdorferi, in Europe. It is common in the damp underbrush of European woods and attacks various domestic and wild animals, including dogs and humans. Lyme disease causes skin lesions, neurological and cardiac abnormalities, and recurrent arthritis. Magnification: x44 when printed 10 centimetres wide.