Do Leeches Always Harm People?

Being bitten by a leech in a tropical environment is not a pleasant experience but the bite is rarely harmful. In fact, leeches have been used in medicine for centuries. In medieval times, blood letting was a common treatment that doctors used to let out 'bad humours' from the blood to cure people of all sorts of diseases.

Whether or not this worked was a bit of hit and miss and people who got better probably would have anyway. However, in recent years, modern day doctors have realised that leeches can help some types of wound, where an accident or animal bite has caused a very traumatic injury with lots of bleeding and clotting, which interferes with healing. Adding leeches to the wound can help clear up the blood from the wound and can help it heal up more quickly.

The anti clotting agent, hirudin, that is produced in leech saliva when it bites has also been used in medicine as a drug to prevent blood clotting after heart attacks and strokes.