The number of adders in the UK has seen significant decline over the past few decades and surveys show that 90% of monitored populations are shrinking – many having fewer than ten individual snakes.
To help combat this issue, ACO Water Management supplied two specially designed snake tunnels in Greenham and Crookham Commons to reconnect two groups of adders that had been separated by a road.
Adders are especially vulnerable when moving across roads as, along with the dangers that passing cars pose, they are particularly exposed to predators. Radio tracking between 2015 and 2022 showed that there were two distinct adder populations present on Crookham Common and Greenham Common, kept apart by Old Thornford Road. Genetic isolation such as this makes species more susceptible to genetic mutations and diseases which can ultimately lead to extinction.
The declining population of adders matters because they contribute to biodiversity and help keep habitats such as heathland in a healthy balance, as well as being a signal of broader environmental degradation.
In 2023, Berkshire, Buckinghamshire and Oxfordshire Wildlife Trust (BBOWT) secured £113,000 from Natural England’s Species Recovery Programme for the Adder Connection project. The funds were designated towards installing two reptile tunnels under Old Thornford Road to reconnect the two separated adder groups. This was the first time such an approach had been attempted in the UK.
ACO supplied two 10-metre tunnels and wing walls to direct the adders toward the tunnel entrances. The tunnels are designed to allow sunlight in – especially important for the cold-blooded reptiles – as well as fresh air and moisture. Removable grates, supplied along with the tunnels, enable easier inspections and maintenance.
Both tunnels were installed in 2024 and lined with a gravel substrate and points where they could take refuge from predators. The areas on each end of the tunnels were improved by removing shrubs and bushes to create basking areas. Logs and brash from the trees which had been cut down to make connecting corridors between open heathland and the tunnels were used to make habitat pile to give the adders extra shelter.
In the autumn of 2024, BBOWT tagged five adders with a small radio transmitter attached to the snakes and tracked their movements. With the seasons changing, minimal movement was expected, although adders were found close to the tunnel entrances. Camera traps were installed to further monitor the adders’ movement and, in the months that followed, picked up rodents, small birds and grass snakes traversing the tunnels.
In April 2025, the camera filmed an adder using the tunnel to pass safely from Crookham Common to Greenham Common, confirming the success of the installation and suggesting that the two isolated groups are now able to interact, adding resilience to the local population.
Long-term monitoring is needed to fully assess the project’s impact into the future, however these early results have shown the potential that projects such as these have to benefit biodiversity and safeguard threatened species.
Terry Wilkinson, Specialist Design & Application Engineer at ACO, said: “It’s been fantastic to be able to contribute to a project that has such a clear and beneficial impact on the local biodiversity. We expect the tunnels we’ve supplied to last for many years and hope to see the adder population return to healthier numbers now that they can move more freely, without having to cross a dangerous road.”
Debbie Lewis, Head of Ecology for BBOWT, said: “The adder tunnels between Greenham Common and Crookham Commons represent an exciting opportunity to reconnect two isolated adder populations, thus helping to ensure a stronger more robust population across the two areas. The ACO tunnels were perfect for the job being robust and easy to install”
For more on solutions that support wildlife and biodiversity, see ACO.co.uk.
