The medicinal leech (Hirudo medicinalis) is the UK’s largest leech species, at 16cm in length when fully extended. It is striking in colour, with stripes of red and yellow set on a black background. As suggested by the name, this is the leech of medieval medicine fame! The leech is still widely used in medicine today, to remove post-surgery swelling or for its anti-coagulent .
Wetlands, ponds and ditches are the habitat of this iconic species. Studies of the blood ingested by leeches did not find evidence of mammalian blood, instead the diet in the wild seems to be mainly amphibian. Reportedly, they can survive drought by burrowing into mud. They are hermaphrodite and lay cocoons amongst the roots of plants such as great willowherb. 
The medicinal leech is a focus species for UK conservation, due to a significant decline in range. Changes in land use, fish introductions, wetland drainage, pesticide usage and loss of grazing have all contributed to this rapid decline . The leech can now only be found in Wales in a handful of sites, including Anglesey Fen .
At North Wales Wildlife Trust Cors Goch on Anglesey, medicinal leech are present. PONT has been involved with conservation grazing cattle here to improve the wetland. The reserve had become rank and dominated by phragmites and bullrushes. For 6 years, cattle and ponies have been grazing here to push back the dominant plants and trample the mat of vegetation back into the fen. This has significantly improved the health of the reserve. This should have knock on effects in improving the habitat for amphibians and as a result, the medicinal leech!
If you require assistance with a conservation grazing project in Wales, please contact PONT. Ausden et al. 2002. The Status, Conservation and Use of the Medicinal Leech. British Wildlife [Link]  Freshwater Habitats Trust  European Community Directive on the Conservation of Natural Habitats and of Wild Fauna and Flora