A tiny and very rare bat could frustrate efforts to build a new relief road for Weymouth in the southwest of England.
The barbastelle bat, which measures just 4.5 centimetres from head to toe, was discovered in a piece woodland next to which the new, proposed highway would run.
One of the rarest species in the UK (Image by BCT/Hugh Clark)
The conservation charity the Woodland Trust is now threatening legal action to stop Dorset County Council approving the transport plans.
The animal, known to scientists as Barbastella barbastellus, is on the government's Biodiversity Action Plan, which means there is official concern about its continued existence in the UK.
It turned up along with other bat species in a survey commissioned by the trust to see what was living in a corner of ancient woodland called Two Mile Coppice.
The trust, which owns the coppice, fears the road could do irreparable damage to what is a Site of Special Scientific Interest.
The current proposals would see the by-pass built on the edge of the woodland and run parallel to a railway line on a raised embankment.
The plans have already been altered once this year to limit their environmental impact - again because of concern about bat roosts.
"The barbastelle is probably one of our rarest species," John Stobart from English Nature, the government's wildlife advisory body, told BBC News Online.
Their pug-like faces made them look ugly to some, he said.
Despite their small body size, a wingspan of around 25 cm enabled them to travel up to 18 kilometres in one night, he added.
Licence to build
No barbastelle breeding roosts have been officially recorded in Dorset and only a single pregnant female was found in a previous study in the county.
Since their calls are silent to us, they are very difficult to track down.
The Woodland Trust survey used high-tech bat detectors to identify calls.
Their survey also picked up the presence of pipistrelle, noctule and possibly even Bechstein's bats in the ancient woodland.
Wild bats in the UK are protected by the 1981 Wildlife and Countryside Act.
Therefore, any development that affects wild bats requires a licence from the Department for Environment, Food and Rural Affairs (Defra).
A spokesperson for Dorset County Council indicated they would seek a licence: "Even if the bats are there, it does not mean that there will be no relief road.
"If the bat presence is confirmed then we will seek a licence from government and the road can still go ahead."
The Woodland Trust plans to commission a more detailed study of the bats in the woodland and says it would consider a legal challenge to any licence.
"The ongoing existence of the ancient woodland habitat will be threatened if the road goes ahead," said Graham Bradley, of the Woodland Trust.
Ancient woodland - defined as land continuously wooded for at least 400 years - now covers just 2% of the UK.
Conservation groups say every effort should be made to protect what remains of "Britain's rainforests", because of the very diverse wildlife they host, such as the endangered dormouse.
The Weymouth relief road is designed to ease congestion into the town. If built it would substantially improve the quality of life for hundreds of people living along Dorchester Road and Preston Road which carry the traffic at the moment.
The escalating costs resulting from environmental concerns have angered local politicians.