Rare blood-sucking leech bred at London Zoo

A rare breed of blood-sucking leech is being bred at London Zoo in a bid to save the UK’s largest native leech species from extinction.

The medicinal leech was once widespread in Britain, but its numbers have declined dramatically due to habitat loss and historic medical use.

There are now just four populations of medicinal leech left in the UK.

London Zoo is breeding the species for the very first time before they are released into the wild to support Britain’s freshwater ecosystems.

"The medicinal leech is one of our most threatened freshwater species. It’s also very misunderstood,” said ecologist Dr Naomi Ewald, from the Freshwater Habitats Trust, a conservation charity behind the project.

“We hope to not only bring this species back from the brink, but also give this wonderful creature a much-needed change of image,” she said.

Medicinal leeches, or Hirudo medicinalis, live in ponds and ditches where they feed on amphibians and grazing animals.

They are also a protein-rich snack for others in the ecosystem.

Their numbers have plummeted in Britain due to changes in land use, freshwater pollution and pesticides.

The species, which is legally protected, can now be found in just 150 ponds across Kent, Hampshire and Dorset, Cumbria and Wales.

Arran Harvey, an aquarist at London Zoo, has overseen the breeding of 68 leeches so far.

The adults are available to view as part of the zoo’s Tiny Giants habitat.

“They're really pretty, a lot more pretty than people would care to think,” said Mr Harvey.

“They’ve got this nice cross-stitch pattern of red and yellow going down their back.”

Mr Harvey feeds them once a month by filling a dried intestine with warm sheep’s blood.

Each adult drinks about 25ml of blood in half an hour, after which they can more than quadruple in size.

“There's no need to worry about being fed on out in the wild,” said Mr Harvey.

"The leeches are so rare, it's probably classed as an honour to be fed on.”

Dr Mike Jeffries, a visiting research scholar at Northumbria University, added: “Evidence of leeches as a treatment date back to 1500 BC, they appear in Egyptian tomb paintings, and in the 18th and 19th centuries a lucrative international market developed."

By the 1800s, leeches were being used as a cure-all for everything from cancer to mental illness.

“While most of these daft treatments were discredited in the early 20th Century, modern scientists have identified more than 100 useful substances in leech saliva, such as anti-clotting and anti-inflammatory agents, antibiotics and anaesthetics,” Dr Jeffries said.

Leeches are still occasionally used by the NHS today to help with blood flow when reconnecting tissue, such as a severed finger, during reconstructive or plastic surgery.

Despite their name, the medicinal leeches at London Zoo are destined for local ponds, not the hospital.

“We've got some parts of the country, like Yorkshire, where they've not been recorded for 100 years, so we'll be able to release them in the future if conditions are right,” added Dr Ewald from the Freshwater Habitats Trust.

“Leeches are like a canary of the pond world.

"If we can get it right for them, then we can get it right for everything else,” she said.

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