Wildlife Guide · Europe & Freshwater wetlands, grazing marshes and ponds
Leech
Hirudo medicinalis Linnaeus, 1758 and related hirudinid species
A blood-feeding worm still prescribed in hospitals — and rarer in the wild than most people assume.
Image: AI-generated educational wildlife portrait — World Animal Rescue Network · AI visualisation, not a photograph
In brief
The medicinal leech (Hirudo medicinalis) is a freshwater annelid worm used clinically to restore venous flow after reattachment surgery, listed as Near Threatened in Europe; leeches are segmented worms related to earthworms, not insects.
By the WARN Research & Conservation TeamChecked against IUCN Red List & CITES sourcesLast updated
Leeches are segmented annelid worms, relatives of earthworms, not insects or molluscs. The medicinal leech Hirudo medicinalis fed European medicine for centuries and returned to modern surgery when clinicians rediscovered its value for relieving venous congestion after reattachment operations — finger, ear and flap surgeries where blood must drain but veins are damaged. Leech saliva contains hirudin and other anticoagulants that keep blood flowing during feeding and after detachment. Wild medicinal leeches are Near Threatened in Europe from habitat drainage and historic over-collection; farmed leeches supply most clinical demand today. Not all leeches feed on blood — many are predatory on invertebrates in freshwater.
Near Threatened
IUCN status for Hirudo medicinalis
Hirudin
Anticoagulant in medicinal leech saliva
Up to ~20 cm
Length of a large medicinal leech extended
Clinical
Still used in reconstructive microsurgery
Figures sourced from IUCN Red List — Hirudo medicinalis, NHS — Leech therapy in microsurgery (overview), Animal Diversity Web — Hirudo medicinalis .
Leech: Quick Facts
| Length | About 6–20 cm when extended |
|---|---|
| Phylum | Annelida — segmented worms |
| Clinical use | Venous congestion after reattachment surgery |
| Saliva | Contains anticoagulant hirudin |
| Habitat | Freshwater marshes and ponds |
| IUCN status | Near Threatened (Hirudo medicinalis) |
Scientific Classification
| Kingdom | Animalia |
|---|---|
| Phylum | Annelida |
| Class | Clitellata |
| Subclass | Hirudinea |
| Family | Hirudinidae |
| Genus | Hirudo |
| Species | Hirudo medicinalis |
Conservation Status
- IUCN Status
- Near Threatened
- Population
- Wild populations depleted in much of former range; no precise global count
- Trend
- Decreasing in wild wetlands; stable in farmed stocks for medicine
- Assessed
- 2014
- CITES
- Not listed
Clinical demand is met largely by farms; wild recovery requires grazing marsh restoration and reduced pollution of pond habitat.
Did you know?
Surgeons still prescribe leeches because nothing synthetic yet matches leech saliva — a wild wetland worm remains part of finger reattachment protocol in modern hospitals.
Key Facts: Leech
- Leeches are annelid worms — segmented like earthworms — not insects or flatworms.
- Hirudo medicinalis is used in modern hospitals to relieve venous congestion after finger, ear and flap reattachment surgery.
- Leech saliva contains hirudin, an anticoagulant that keeps blood flowing during and after feeding.
- The medicinal leech is Near Threatened in Europe from wetland drainage and past over-collection.
- Not all leeches are blood-feeders; many freshwater species hunt invertebrate prey.
- Farm-raised leeches supply most clinical use; wild populations remain depleted in parts of the range.
Why surgeons still order leeches
Reattached tissues need arterial inflow and venous outflow. When veins are crushed and cannot drain, blood pools in the digit or flap and the tissue dies. A leech removes congested blood and injects anticoagulants that prolong local bleeding slightly — paradoxically saving the graft by preventing clot backup. Treatment uses sterile farmed Hirudo medicinalis under supervision. Several leeches may be applied over days. The practice is not medieval relic; it is standard in reconstructive microsurgery units. Synthetic anticoagulants cannot fully replicate the combination of effects in leech saliva.
Feeding and anatomy
Blood-feeding leeches detect hosts by movement and chemical cues, attach with suckers at both ends, and slice the skin with three jaw blades. Saliva delivers anaesthetic and anticoagulant compounds. A full meal can last the leech months; medicinal leeches take a single large blood meal then digest slowly. Predatory leeches swallow whole prey — chironomid larvae, snails — without the blood-feeding specialisation. Identification requires habitat and mouthpart detail; the name 'leech' covers hundreds of species with different diets.
Wetland loss and Near Threatened status
Hirudo medicinalis lived in grazing marshes, fens and ponds across Europe. Drainage for agriculture, eutrophication and historic collection for medicine reduced wild populations sharply. The IUCN lists the species as Near Threatened. Conservation combines habitat restoration — seasonal grazing marshes with cattle poaching — with regulated farming for medical supply so wild collection pressure stays low. A species can be clinically indispensable and ecologically depleted at the same time.
Separating leeches from myths
Leeches do not invade human bodies routinely; they attach externally and drop off when full. Tropical land leeches in rainforest leaf litter are a different experience for walkers but still external feeders. Leech therapy in unregulated settings risks infection and is not the same as hospital use of farmed Hirudo. Earthworms are also annelids but lack suckers and blood-feeding jaws. Medicinal leech identification uses banding pattern, size and habitat — specialist knowledge matters because not every pond leech is Hirudo medicinalis.
What WARN Does
WARN publishes sourced education for species whose wild populations decline while clinical demand continues. Medicinal leeches illustrate how wetland loss removes organisms that modern medicine still relies on — often from farms descended from wild stock.
If this guide helps you understand wildlife and the pressures it faces, a gift to WARN supports habitat protection and free public education in our partner countries.
How can I help save the leech?
There are three practical things that make a real difference for the leech — and the first is the one that funds everything else.
Fund frontline rescue
Back the partner-led teams, veterinary care and protection that reach leechs where the need is greatest — WARN channels donations straight to that work.
Ease the pressures
Avoid the wildlife trade and souvenirs, never buy wild animals as pets, and choose sustainable, habitat-friendly products — the threats behind the leech's decline fall when demand does.
Spread the word
Share accurate, sourced information about the leech. Wider awareness is what turns concern into lasting protection.
Leech: Frequently Asked Questions
How can I help save the leech?
What do leeches eat?
Where do leeches live?
Are leeches dangerous?
How long do leeches live?
How big are medicinal leeches?
Why are leeches used in hospitals?
Are leeches endangered?
Sources & References
Population figures, conservation status and biological facts on this page are drawn from authoritative scientific and intergovernmental sources.
Terms used on this page
Plain-English definitions, from our wildlife and conservation glossary.
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