Deep in the forest there are man-made ponds that hum with wildlife. Dragonflies and damselflies dance at the edges and beetles and lizards scurry below, the sights and sounds of summer.
In many of the pools, however, a creature lurks that has 10 eyes, 300 teeth and a taste for human blood. By the largest pond, a sign warns, “Beware the blood suckers”.
For decades, Newborough Forest, Anglesey, has been one of the few sites in Britain where the medicinal leech is still found. Yet even here their habitats are shrinking as ponds silt up and vegetation encroaches.
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Over the past three years conservations have bitten the bullet and re-profiled some of the forest ponds. For some, the sight of diggers and bulldozers has been un-nerving, the roar of engines replacing the gentle buzz of insects.
The work was undertaken by the EU-funded Sands of LIFE (SoL) project and the land management team at Natural Resources Wales (NRW). SoL project manager Kathryn Hewitt said the work was necessary – to safeguard existing rare species, such as leeches and great crested newts, and to expand the forest’s biodiversity.
“Some species were in danger of disappearing as the pools filled up,” she said. “By enlarging the ponds, removing invasive alien species and old conifer stumps, and scraping back the edges to expose sand, we will be able to manage these areas to maximise biodiversity.”
Earlier this month, as Newborough basked in a mini-heatwave, Kathryn stripped off her shoes for a quick cool-off in Pwll Pant Mawr, the largest of Newborough’s ponds. She quickly stepped back. “A leech in the water was making straight for me!” she shuddered.
Leeches have three jaws, each with 100 teeth, that leave a distinctive bite mark, as if made by a circular saw. These creatures are the stuff of nightmares – other alien-like attributes include 10 stomachs, 32 brains and nine pairs of testicles. Usually, however, they are perfectly harmless beyond some painless bleeding.
In Newborough Forest, it’s not the walkers who need to worry. An information board on the Bike Quest Nature Trail explains who the local leeches like to target.
“They are very rare because most people don’t want them sucking their blood anymore,” it says. “Our leeches are fit and healthy because they have a good bit of horse blood from when the horses go into the ponds for a drink.
“This doesn’t hurt the horses but it does wonders for our leeches!” The horses are in fact wild ponies, brought in to graze the glades to prevent them from returning to woodland.
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Other potential victims include water-loving dogs that can’t resist a dip. Here, however, the boot is firmly on the other foot. Flea and worming treatments than enter leech habitats have decimated populations since the 1970s and conservationists fear their work at Newborough could be undone by freshly dosed canines.
On social media last week, the Sands of LIFE project pleaded: “Veterinary flea treatments are now known to cause water pollution and kill off rare invertebrates like leeches. So please don’t let your dog play in pools on the dunes.”
Dog owners living on Anglesey have also been warned to take extra care when visiting beaches and stagnant ponds. It follows a mysterious spate of illnesses in which at least one dog has died. You can read more about this here.
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After World War 11, Corsican and Scots pine were planted on Newborough Warren’s shifting sands, partly to protect the village. Amid concerns of falling water levels in the forest, trees were cleared in the 1960s and 70s to create glades.
Within these, ponds were dug both for wildlife and as natural reservoirs in case of fire. These relic habitats on former dunes boosted local biodiversity – orchids being among the beneficiaries – but only years later was it realised their banks were too steep for wrigglers like leeches.
As part of the recent remodelling, several ponds was scraped back to produce shallow sandy “beaches”. They’ve also been deepened to ensure they don’t dry out in summer, as had been happening. At Pwll Pant Mawr, 21,000 tonnes of sand were removed.
“The work was carried out in stages over three years to avoid disturbing important areas for resident species,” said Kathryn. “This also allowed us to see if adjustments were needed as we went along.”
By the middle of the 19th century, tens of millions of British leeches were being exported to Europe and America each year. There were few illnesses for which they were not recommended, physicians believing they could remove “bad’ blood” that caused sickness.
More recently, chemicals, veterinary medicines, loss of grazing and wetland drainage have all driven further declines. The work at Newborough aims to stem the process by creating a leech haven.
If, as hoped, numbers continue to increase, it’s unlikely any will ever be put to medicinal use (leeches are still employed in some clinical settings). But it’s not impossible.
“By increasing biodiversity, you increase genetic diversity,” said Kathryn. “If ever there was a problem with commercial stocks (of leeches), our wild strains can provide new genetic material.
“It’s the same idea as preserving wild strains of bananas and coffee, should anything ever happen to commercial stocks.” So, the next time you go down to the woods, keep an eye out for the “blood suckers” but treat them with respect.
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