Love the languid leech

I got a worried call from a neighbour the other day. There were leeches in his garden pond. Big ones.

I reassured him he wasn’t going to get nasty blood-sucking creatures attached to him every time he did pond work. There is only one species of leech in this part of the world that can do that, the medicinal leech, and it appears to have become extinct in Ireland over 100 years ago.

There are still a few wild populations left in Britain and on the Continent but it’s classified as an endangered species and there are special conservation measures to protect it. There are about a dozen other species of freshwater leech found here, and a few salt- water ones off the coast. They are all harmless to humans, though some could attack water fowl, goldfish or frogs in a pond.

The ones in my friend’s pond were horse leeches (which don’t attack horses or people but prey mainly on water snails). Leeches are related to earthworms and the horse leech can grow to the size of a large lob-worm —- about 15cm long. They are a green/ brown colour and, unlike worms, they are not round in section but flattened or oval.

They swim with an odd pulsing movement that changes their shape and they have jaws and suckers at each end. Occasionally they turn up in damp places on land, sometimes a long way from open water.

The medicinal leech gets its name from the ancient practice of attaching leeches to sick people in the belief that they would suck the disease out of them, along with their blood.

Over a century ago medical science dismissed this therapy as being useless and possibly dangerous. However, it’s still offered by a small number of practitioners of alternative medicine in this country.

Because medicinal leeches are protected in the wild and trading them is banned, the alternative medicine people get them from leech farms. There are several in Europe, including a large one in Wales. But the farms don’t depend for their livelihood on alternative medicine. Although bloodletting is now frowned on, leeches and extracts from leeches are still used in some sophisticated medical therapies, including the reattachment of severed limbs and cardiac medicine.