The Medicinal Leech is a blood-sucking worm with a flattened segmented body. It can be found scattered around England in muddy ponds and pools which have lots of waterweeds. It has its name the ‘Medicinal Leech' because for centuries it has been used for medicinal purposes, like for removing ‘bad blood’ or to ‘treat headaches’. Nowadays, it is mainly used to restore blood circulation after a patient has had a tissue graft or reconstructive surgery.

The Medicinal Leech is usually about eight centimetres long and has a dark brown or black body with orange-red lines running down it. Its body is divided into approximately thirty-four segments and it has five pairs of eyes situated on the first five segments. The Medicinal Leech has a ‘sucker’ at the end of its tail and one on its head. It uses the suckers to attach itself to an animal so it can suck some blood out of it. The sucker on the head surrounds the Medicinal Leech’s mouth which has three sets of jaws. The leech uses these jaws to bite into an animal and then releases saliva which can deaden the pain of the bite. When the Medicinal Leech has taken enough blood, it drops off into the water and it may not need to suck blood again for another six months.