Under the graveyard sleep the bats

Arnos Vale, Bristol Bats are very particular about their living conditions and every breath we exhale will gradually alter the humidity of their home

There's something about graveyards that makes me stare at my feet. It's partly respect for other visitors but also a morbid fascination with what I'm walking across. I imagine layers of gothic decay: bones, beetles and things that go bump.

So when I'm invited under the gatehouse of Bristol's Arnos Vale Cemetery by a grave digger turned ecologist, my expectations are set to spooky. The screech of an electric drill sounds as the groundskeeper unscrews a protective wooden panel and I descend into the pitch-black basement. The tunnel here was once used by Victorian undertakers to travel between the entrance buildings without disturbing mourners: now it's home to rare mammals. At the bottom of the stone steps I duck my head under an archway and immediately spot what we're looking for: a black diamond shape suspended from the ceiling.