Species on the Edge is delighted to be working with the Royal Zoological Society of Scotland (RZSS) to boost the number of a species currently teetering on the edge of extinction in Scotland. Having faced overharvesting for medical reasons in the 18th and 19th centuries and now being further impacted by habitat loss and pollution, this species now has only three known populations in Scotland. Have you guessed what this species is yet? It’s the fascinating medicinal leech.
Medicinal leeches can grow up to 20cm long making them one of the UK’s largest native leeches. They can be found in a variety of freshwater habitats, including ponds, lochs, ditches, wetlands, and streams. In Scotland, medicinal leeches have a dark brown or black upper side with yellow-grey stripes and a speckled underside. They feed on blood from cattle, deer, amphibians, fish, and birds, and only feed every 3 to 12 months. They can live up to 20 years.
Medicinal leeches have a fascinating biology. Individual medicinal leeches are both male and female at the same time, have a ‘brain’ in each of their body segments, have five sets of eyes, two suckers (a posterior back sucker used as leverage to move and a front sucker used for feeding), can go without feeding for weeks, and live exclusively on blood.
Once widespread, the medicinal leech is now known in only three areas in Scotland – mainland Argyll, Islay, and now Dumfries and Galloway – having suffered severe declines primarily due to historical overharvesting for use in medicine. In the late 18th to early 19th century, millions of these leeches were used in hospitals across Europe for bloodletting treatment. While medical exploitation of the leech is now illegal in the UK, habitat loss and freshwater pollution have badly affected Medicinal Leech populations in Scotland.
Through Species on the Edge, Buglife is working with the Royal Zoological Society of Scotland (RZSS) to deliver Scotland’s first ever medicinal leech conservation breeding programme. In an effort to save the rare leech from extinction in Scotland, 14 leeches have been collected from one of their known sites and transferred to their new home – a specially designed facility at RZSS’s Highland Wildlife Park. There the conservation team staff have been caring for them and attempting to breed as many leeches as possible to then be released back into the wild.
And we’re delighted to say that, so far, the programme has been a success! In July 2024, the team at the Highland Wildlife Park reported that the leeches had started to produce egg cocoons, and in August 2024 came the fantastic news that the eggs had hatched! The next stage will be to start new populations in suitable lochs around the country. We’ll keep you posted!
It’s a very exciting project with many people helping out. Let’s hear from some of the team:
“Medicinal Leeches have an important place in our medical history but are now one of the rarest invertebrates in Scotland. Conservation breeding was first suggested for this species nearly 30 years ago. It’s fantastic that the Species on the Edge project means that we can now take this important step to secure the future of the Medicinal Leech in Scotland.” – Craig Macadam, Conservation Director at Buglife.
“Medicinal leeches have a fascinating history and form part of complex freshwater ecosystems, but people can be a bit grossed out by the whole blood-sucking thing. They are certainly very different from any other animal we look after in the conservation department, but that just makes them more interesting. We are excited to be looking after such an unusual species, and to be helping secure a long-term future for them in Scotland through our dedicated conservation breeding and reintroduction programme.” – Dr Helen Taylor, conservation programme manager at RZSS
If you see a large leech in Scotland, please take a photo and send your sighting to Buglife at scotland@buglife.org.uk. Please note they are rare and protected, so if found attached to waders or wetsuits please gently brush them off and return them to the water.
