Medicinal leech-Hirudo medicinalis

Mediicinal leech - short anatomy

The medicinal leech (Hirudo medicinalis) has a slightly flattened cylindrical body, divided into 33 or 34 segments. The upperside is dark brown or black with six long reddish stripes, whilst the underside is speckled. There is a disc-shaped sucker at the head end. The leech is famous for sucking blood and the 'mouth' of the animal is situated within the sucker, complete with teeth. The leech also has five pairs of eyes.


Leeches feed on blood

Having attached itself to the host animal, it pierces the skin and injects an anaesthetic to hide the pain of its bite so that the host does not find the leech and remove it, and an anticoagulant chemical, which prevents the host's blood from clotting whilst the leech feeds. The length of time a leech may feed seems to vary. One surveyor, as an experiment, allowed a leech to feed on him and it fed for 83 minutes.

Leeches find their host animals by detecting disturbance in the water, and they can prey on small creatures as well as large. A frog or a newt, for example, can die from excessive blood-loss following an attack by a leech. Leeches may also behave as predators on some species of fish such as sticklebacks, as well as on great-crested newts and marsh frogs.