The horse leech (Haemopis sanguisuga) is a large, native UK freshwater invertebrate commonly found in ponds, ditches, and slow-moving waters. Despite its name, it does not suck blood like some other leeches. Instead, it is a predatory species, feeding on small invertebrates such as worms, insect larvae, and snails they are excellent scavenges of dead animals. It can grow up to 15 cm long and is typically dark brown or greenish in colour. The horse leech moves with a looping motion and swims with a snake-like undulation. It plays a role in pond ecosystems as both predator and prey, contributing to the balance of aquatic life.