A pair of hibernating grass snakes were spared a rude awakening after being discovered by Crossrail workers clearing a site in Berkshire.
Work by contractors around Trenches footbridge in Langley halted as Network Rail sought advice from an ecologist.
The snakes were transferred to a newspaper-lined bucket with vegetation to ensure they did not wake up.
The newly named Jack and Joe have been temporarily moved to a specialist reptile centre in Newport, Wales.
The pair, who are not poisonous and are native to Britain, were slowly woken up and will be fed throughout the winter.
They will be returned to the countryside near Trenches footbridge at the end of March.
Jason Hamilton, Network Rail project manager, said: "Before we started at Trenches bridge we undertook a full ecological survey and found no signs of reptiles, but when you're dealing with nature, unexpected things can happen."
Grass snakes are usually found near water and it is rare to see them during the winter when they hibernate.
The UK population is estimated at 180,000 according to the Surrey Amphibian and Reptile Group (SARG).
Trenches footbridge is being replaced as part of the Crossrail programme, which will provide a new electric rail service for Slough residents into central London.
The old bridge was demolished over Christmas and the new one will be installed over Easter.