The Medicinal Leech (Hirudo verbenaand Hirudo medicinalis) is an invertebrate parasitic worm, and an annelid. It is related to the earthworm. It is called medicinal because doctors have used the leech to draw blood from patients.
There are two types of true leeches: Rhynchobdellida (with a proboscis to puncture the skin of animals) and Arhynchobdellida (without a proboscis). The Medicinal Leech (Hirudo verbena) is a Arhynchobdellida Hirudiniformes (a leech without a proboscis, but with jaws at the front of the mouth).
The Medicinal Leech has a flat, soft, muscular, segmented body without a backbone or skeleton. Therefore, it is an invertebrate. Its upper part is grey with pinkish stripes, or mottled grey-pink-brown, and its underbelly is pale-grey. Its body can lengthen and contract (i.e. get bigger and smaller) as it moves. It has suckers on it mouth and its tail end (anterior and posterior suckers).
It measures up to 15 centimetres (6 inches) long.
The Medicinal Leech is aquatic, living in water. It lives in freshwater, unlike other leeches that live in marine (saltwater) or terrestrial (land) environments. It lives in damp places in ponds, ditches, and other water sources in tropical regions.
It can feel the touch and vibrations from nearby animals. It likes the dark, and avoids light. It moves using its muscles and suckers in an inching way – first stretching out and attaching its sucker to the ground, then lifting up its body and contracting it (like a caterpillar).
It is parasitic and haematophagous, meaning that it feeds on blood. It attaches a sucker to an animal, usually a hoofed mammal, when it comes to drink from the water source. First it inserts saliva into the animal to prevent the blood from clotting (hardening). It usually only feeds twice a year, taking months to digest the blood.
The Medicinal Leech is hermaphroditic, because it has both male and female reproductive organs. Leeches interwine around each other when mating. It lays eggs out of the water, in a spongy cocoon, which is attached to a fish, called the host. There are about 12 eggs. When they hatch, fully-formed baby leeches emerge.
Photographer: Martina Nicolls
Martina Nicolls: SIMILAR BUT DIFFERENT IN THE ANIMAL KINGDOM