Ixodes ricinus (often known as the Sheep Tick) occurs widely in relatively humid, cool, shrubby and wooded pastures, gardens, windbreaks, floodplains, and forest through much of Europe to the Caspian Sea and northern Iran, as well as in northwestern Africa. Its life cycle requires two to four years, depending on temperature. (In drier, warmer, eastern Mediterranean regions, I. ricinus is replaced by I. gibbosus, which completes its life cycle in just one year.) Ixodes ricinus larvae feed on small reptiles, birds, and mammals. Nymphs feed on small and medium-sized vertebrates and adults feed mainly on mammalian herbivores and livestock. All stages, especially nymphs and adults, parasitize humans. Male I. ricinus take little or no food, but mate on the host while the female feeds. Adult activity peaks in spring; in some populations, there is a lower peak of adult activity in the fall. Among the numerous diseases transmitted by I. ricinus to domestic animals and humans are tickborne encephalitis, Crimean-Congo hemorrhagic fever, ovine encephalomyelitis, Lyme disease, babesia, and anaplasmosis. (Merck Veterinary Manual online)
Ixodes ricinus is well known as an important vector in Europe of Lyme borreliosis (Lyme Disease), the most prevalent tick-transmitted infection not only in this region but, more generally, in temperate areas of Europe, North America, and Asia. (In the eastern United States and western United States, the main Lyme disease vectors are the related ticks I. scapularis and I. pacificus, respectively.)
There is a clear correlation between the increase in the USA and much of western Europe in abundance of deer (the main hosts for adult I. scapularis [in the eastern United States] and I. ricinus [in Europe]) with tick density. This is due to conversion of agricultural land into habitat suitable for the maintenance of large populations of deer. (Jongejan and Uilenberg 2004)
