Medicinal Leech

Hirudo medicinalis, the European medicinal leech, is a blood feeding annelid in the class Clitellata and family Hirudinidae, formally described by Linnaeus in 1758 and one of several leech species used therapeutically. Adults reach about twenty centimetres in length, coloured green, brown or greenish brown with a darker back and lighter underside and a thin red stripe along the dorsal surface, and have two suckers, an anterior sucker containing tripartite jaws lined with roughly one hundred sharp edges and a posterior sucker used for attachment; a feeding bite leaves a distinctive inverted Y mark inside a circular wound. A single feeding can draw up to ten times the leech's own body weight, typically five to fifteen millilitres of blood, after which it may go up to a year before feeding again. The species ranges across nearly all of Europe into parts of Asia, reaching Kazakhstan and Uzbekistan, favouring muddy freshwater pools and ditches with abundant vegetation in temperate regions, though nineteenth century over-collection and habitat loss have left it listed as Near Threatened by the IUCN. Ancient Egyptian medical texts describe leech therapy from three thousand five hundred years ago, and medieval European medicine used leeches for bloodletting; modern medicine revived their use in the 1970s for microsurgery, particularly finger reattachment and reconstructive procedures, drawing on secretions in their saliva that promote blood flow and reduce inflammation.