Latin name: Hirudo medicinalis
Notable feature: The largest leech found in the United Kingdom
Conservation Status: Near Threatened
Where in the UK: There are around 20 isolated populations from Kent, Hampshire and Cumbria in England, Powys, Glamorgan and Anglesey in Wales, and Argyll and Islay in Scotland. It is now considered extinct in Ireland.
Medicinal Leech (Hirudo medicinalis) © Roger Key
The Medicinal Leech (Hirudo medicinalis) is the largest, native leech found in the UK. Found in a limited number of locations in freshwater, usually in small pools with muddy bottoms and fringed with reeds.
The Medicinal Leech has a slightly flattened, cylindrical body with a dark brown or black upper-side. Populations in England and Wales are patterned with red and yellow stripes on their dark upper-sides. In Scotland the upper-side has darker yellowish-grey stripes.
The Medicinal Leech has five pairs of eyes.
- Size: Up to 20cm in length
- Life span: Up to 20 years
- Diet: Medicinal Leeches typically feed on blood from mammals such as deer, sheep and cattle which enter the water to drink. Juvenile leeches will feed upon the young of frogs, toads and newts. Once fully fed, an adult leech may not feed again for 12 to 18 months
- Reproduction: Medicinal Leeches are hermaphrodites and reproduce in late summer. They lay spongy cocoons below stones on the shore or amongst plant roots just above the water. They take at least two years to reach breeding maturity, but this may take as long as four years.
- When to see: Medicinal Leeches are strictly protected so it is an offence to handle them without a licence.
- Population Trend: Declining. Medicinal Leeches were used extensively in medicine historically and many wild populations were exploited to supply leeches for bloodletting. As a result, it is now rare throughout its range in Europe and extinct in much of its former range, with the IUCN categorising it as globally Near Threatened due primarily to the overharvesting of leeches in the past for medical use. The proportion of each population that are of breeding size is often quite low and removal of large leeches for medicinal use may have had a disproportionate effect. Such exploitation is now illegal in the UK as the Medicinal Leech is fully protected on Schedule 5 of the Wildlife & Countryside Act.
- Threats: Loss of wetlands habitats, changes to grazing regions and declines in amphibian populations, both of which can reduce the availability of hosts for a blood meal, and the use of anti-helmintic veterinary medicines.
- Fun Fact: A related species, the Mediterranean Medicinal Leech (Hirudo verbana) is still used by health care professionals. There’s even a leech farm in Wales to ensure a supply of these medical helpers.
- Bonus Fun Fact: In Medieval times doctors were often called ‘leechs’ because they would prescribe Medicinal Leeches as a cure for many ailments. The medical connection may go back further though – the Gaelic word ‘lighiche’ means healer or physician.
How you can help:
Buglife is working to increase awareness of invertebrates and the Medicinal Leech through specific projects, such as Species on the Edge, and campaigns, but we need your help!
Join a recording scheme and log your finds – Buglife welcomes records of Medicinal Leeches, look out for large, well-marked leeches in shallow lakes and pools. Also, make sure you report any suspicious behaviour beside rivers, in particular anyone handling/collecting leeches from freshwater habitats; reports should be made to your local Police Wildlife Crime Officer
Do remember that we rely on donations to continue our work. If you have searched, found and learnt about our incredible invertebrates on our website, please do consider Making a Donation, Becoming a Member or maybe even making a purchase in our shop. For more ideas on how to support our work find out how to Get Involved. Thank you 🕷