Medicinal Leech breeding success could save species from extinction

Efforts to save an iconic British freshwater species from extinction have been boosted by news that a small population of Medicinal Leech is now breeding, for the first time, at London Zoo. 

Led by national wildlife conservation charity Freshwater Habitats Trust, the Medicinal Leech Recovery project is taking practical steps to halt and reverse the decline of Hirudo medicinalis, the UK’s largest native leech. This includes establishing a small breeding population at London Zoo. Since taking the leeches into its care, London Zoo has successfully bred over 40 young Medicinal leeches, marking a huge conservation success for the species. 

The number of Medicinal Leeches in Britain has declined dramatically and the species is now on the brink of extinction. Once found in high abundance at hundreds of sites, there are now only four main populations left, in Kent, Hampshire and Dorset, Cumbria and Wales.  

The Medicinal Leech is entangled in British medical history. During Medieval times, when leeches were common, they were often used as a medicinal cure. Leeches are still essential for medicine and are used to increase blood circulation. 

The native leech’s decline was initiated by the historical medical trade, when millions of leeches were exported abroad. More recently, changes in land use, wetland drainage and loss of grazing have contributed to losses. 

Freshwater Habitats Trust is working with partners, including London Zoo, to understand more about the elusive invertebrate and to establish a breeding population. Scientists from Freshwater Habitats Trust and ZSL have been monitoring the leeches in their remaining habitats and gathered a small number to be cared for at London Zoo. 

The population is thriving in its new home, under the care of the conservation Zoo’s expert animal care team. Visitors to London Zoo can see some of the adult leeches in Tiny Giants – a habitat dedicated to tiny creatures with a big impact.The project partners are now investigating future opportunities to reintroduce some of the animals to sites across the country. 

Freshwater Habitats Trust and partners are also carrying out research, including trialling the use of environmental DNA (eDNA) to monitor the species in the wild. Efforts to save the Medicinal Leech are made more challenging because the creature is notoriously difficult to track: it only occasionally comes out to feed and leaves very little trace in the water.  

Dr Naomi Ewald, Technical Director at Freshwater Habitats Trust said: “The Medicinal Leech is one of our most threatened freshwater species. It’s also very misunderstood. Through this project with London Zoo and other partners we hope to not only bring our native Medicinal Leech back from the brink of extinction, but also give this wonderful creature a much-needed change of image. 

“The threats facing the Medicinal Leech are the same as those for other freshwater species. Freshwater wildlife needs unpolluted, high quality habitats to survive and sadly these are now increasingly scarce. Declining water quality and changing land-use have pushed this species to the edge.  

“We are absolutely delighted that the leeches have settled so well into their home at London Zoo and are now breeding. This gives us hope that we can halt and reverse their decline.” 

Dave Clarke, Lead Zookeeper for Ectotherms at London Zoo, said: “This collaborative conservation initiative with Freshwater Habitats Trust demonstrates the power of conservation zoos to reverse biodiversity loss. With the UK’s freshwater wildlife under ever-increasing threat, the young leeches are a significant conservation success and represent hope for further conservation of this iconic but often misunderstood species. 

“The leeches are thriving at London Zoo – we hope their presence will raise awareness of the need to protect the UK’s freshwater habitats and help bring this species back from the brink of extinction.” 

The native British Medicinal Leech has striking vivid orange, red and yellow markings. It is found in ponds and ditches, where it commonly feeds on amphibians and grazing animals visiting the ponds. Medicinal leech in turn, provide an important protein rich meal as part of the food web for other animals.