Snails with legally protected status could delay a road scheme by five years as a project to rehome them is kept under observation.

Ditches alongside a section of the A47 in Norfolk are a habitat for little whirlpool ramshorn snails, whose shells measure just a few millimetres in diameter.

The rare freshwater species is protected under the EU habitats and species directive. Any significant work to the section of the A47 between Acle and Great Yarmouth, including erecting safety barriers, is likely to disturb the snails and therefore needs a licence. This requires demonstration that “favourable conservation status” of the species will be maintained.

Eight hundred of the snails were moved from the ditches to a new habitat in 2016, and more were relocated in 2017 and this year. The snails will be monitored until 2023 before Highways England can determine whether the translocation project has been a success.

A Highways England spokesman said: “Environment surveys revealed the rare and protected little whirlpool ramshorn snail made its home in ditches alongside the Acle Straight section of the A47, meaning they will need to be successfully relocated before any future scheme can be considered along this section of road.

“Highways England are currently undertaking a translocation project and early indications suggest the translocation of these rare snails has been successful and we will continue to monitor them in their new location for a number of years to come.

“The A47 remains an important route for Highways England, and we will continue to assess where improvements are needed and can be delivered in an environmentally responsible way.”