INTRODUCTION same 800 species of ticks, in three families, exist throughout the world. Twenty-three species from two families are found in the British Isles, the majority of which belong to the family Ixodidae, or hard ticks, and in particular to the genus Ixodes. Hard ticks are characterized by the possession of a sclerotized scutal plate on the dorsum and by having terminal mouthparts. The Argasidae or soft ticks, of which only three species have been recorded in the British Isles, do not have this dorsal scutum and have mouthparts positioned ventrally and therefore not visiblefrom above.

There are four stages in the life cycle of a tick: an egg, a six-legged larva, an eight-legged nymph (which in the argasids may have anything up to eight morphologically similar instars), and an eight-legged, adult stage. All mobile stages, except the males of a few species, feed on blood and/or tissue fluids. In some species, the immature stages may feed on a different host species, species group or even phylum to that of the adults; for example, the larvae and nymphs of Haema h salis unctata feed on small mammals and birds, while the adults are mainly found on large mammals.