London Zoo Breeds Rare Leech to Combat Extinction

A rare type of blood-sucking leech is currently being bred at London Zoo as part of an initiative to prevent the extinction of the UK’s largest native leech species. The medicinal leech, once prevalent across Britain, has seen its numbers decline significantly due to habitat destruction and its historical use in medicine. Only four populations of medicinal leech now exist in the UK. This marks the first time London Zoo has undertaken breeding of this species, with the aim of releasing them into the wild to bolster Britain’s freshwater ecosystems. Ecologist Dr Naomi Ewald, from the Freshwater Habitats Trust, a conservation charity involved in the project, commented, “The medicinal leech is one of our most threatened freshwater species. It’s also very misunderstood.” She added, “We hope to not only bring this species back from the brink, but also give this wonderful creature a much-needed change of image.” Medicinal leeches, scientifically known as Hirudo medicinalis, inhabit ponds and ditches, where they consume amphibians and grazing animals. They also provide a protein-rich food source for other components of the ecosystem. Their populations in Britain have plummeted due to changes in land use, freshwater pollution, and pesticides. The species, which benefits from legal protection, is now found in merely 150 ponds across Kent, Hampshire and Dorset, Cumbria, and Wales. Arran Harvey, an aquarist at London Zoo, has supervised the breeding of 68 leeches thus far. The adult leeches are on display within the zoo’s Tiny Giants habitat. Mr Harvey remarked, “They’re really pretty, a lot more pretty than people would care to think.” He described their appearance: “They’ve got this nice cross-stitch pattern of red and yellow going down their back.” Mr Harvey feeds them monthly by filling a dried intestine with warm sheep’s blood. Each adult ingests approximately 25ml of blood in half an hour, after which their size can more than quadruple. “There’s no need to worry about being fed on out in the wild,” stated Mr Harvey. He further noted, “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 utilized as a panacea for conditions ranging from cancer to mental illness. Dr Jeffries explained, “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.” Today, the NHS still occasionally employs leeches to assist with blood flow during tissue reconnection, such as a severed finger, in reconstructive or plastic surgery. Despite their nomenclature, the medicinal leeches at London Zoo are destined for natural ponds, not medical facilities. Dr Ewald from the Freshwater Habitats Trust elaborated, “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.” She likened leeches to a vital indicator: “Leeches are like a canary of the pond world.” She concluded, “If we can get it right for them, then we can get it right for everything else.”