Lyme disease tick. Computer illustration of a female Ixodes ricinus tick, a blood-sucking parasite of humans and the principal vector of Lyme disease in Europe. This tick uses specialised mouthparts to pierce the host's skin and hold fast for several days while it swells with blood, increasing in weight by up to 200 times. The female feeds only three times during her life and can survive for years between meals, spending most of the time hidden in vegetation. Mating takes place just before her final meal, after which she drops to the ground and lays thousands of eggs. I. ricinus transmits the bacterium Borrelia burgdorferi to humans, which causes Lyme disease.