Britain has constructed its first adder tunnels to help these venomous reptiles safely cross roads, aiming to increase their population after recent declines.

The two trenches, topped with cattle grid-like grates, allow sunlight to penetrate, which is crucial as adders rely on external heat sources. This initiative by the Berkshire, Buckinghamshire, and Oxfordshire Wildlife Trust was prompted by the discovery that a road through Greenham and Crookham Commons was preventing mating between two distinct adder populations.

Debbie Lewis, the trust’s head of ecology, highlighted the importance of genetic mixing between these isolated groups.

“They are a part of our native biodiversity and could be extinct here in 10 to 15 years if we don’t do anything,” she said.

Monitoring with radio trackers revealed that adders approached the road but did not cross it, indicating the road was a significant barrier.

Adders (Vipera berus), identifiable by their zig-zag patterns, are shy and cold-blooded reptiles. They inhabit woodlands, heathlands, and moorlands, and need sunlight to warm up. They hibernate from October to March.

Currently found in England, Scotland, and Wales, they are absent from Northern Ireland. A 2019 study warned that adders could disappear from the British countryside by 2032.

“They don’t like people so they’re more likely to disappear,” said Mrs Lewis. “The chances of you seeing them are very slim. They can feel you approaching through the vibrations in the ground and are likely to stay away.”

The new tunnels are also expected to benefit other small mammals and reptiles. While sightings of adders are rare, the public is advised to observe them from a distance due to their venom.

“They are venomous. Admire from a distance but don’t disturb them.”

Adder bites, though painful, are mainly dangerous to the very young, elderly, or those with health issues. The last fatality from an adder bite in the UK was recorded in 1975.

Funding for the tunnels came from Natural England’s Species Recovery Programme, established 30 years ago to support threatened native species. The success of this initiative is still being monitored by the trust in Berkshire.

For now, the trust must wait to see if these tunnels effectively facilitate genetic mixing and population growth among the adders.

“The two populations weren’t mixing before so hopefully they will now,” Mrs Lewis said. “It’s a bit of a trial as there are snake tunnels in other countries but not in the UK, this is the first one.”



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