Leeches are segmented worms with flattened bodies. They are usually black or brown, although some species are brightly colored. Many leeches have attractive speckled or striped patterns. They are amazingly flexible, able to expand and contract to the point where it’s difficult to measure them. Each body segment is subdivided into “annuli,” which resemble wrinkles and add to the creature’s flexibility. There is a sucker at each end of the elongated body, and the suckers are often used for locomotion: Leeches can move by “looping” like an inchworm. The “head” of a leech holds the mouth sucker, usually at the more tapered (narrower) end, and about a quarter of the way down from this is the clitellum, which becomes more noticeable during times of reproduction (earthworms have this same swollen-looking structure).