A colony of cave spiders have been found in the grounds of the John Innes Centre at Norwich Research Park.
Cave spiders aren't rare but you don't often see them because they're photophobic which means they don't like light and so seek out moist, dark conditions.
Pip Collyer, a spider expert from the British Arachnological Society, said: "It's one of the bigger spiders we have in this country.
"It obviously doesn't like the daylight. It lives its life in total darkness and there are probably more colonies of these than we realise because people are not looking in sewers or culverts or tunnels for them."
It's extremely difficult to distinguish from the Meta Menardi cave spider and the rarer Meta Bourneti spider. The spiders found at the John Innes Centre are the rarer variety.