Found – The spider that was feared extinct in the UK

Rossers Sac spider, found at Lakenheath fen. Photo copyright Peter Harvey.

November 201. These are the first pictures ever taken of the Rosser's sac spider. An incredibly rare creature that some scientists feared was extinct in Britain. It's ten years since the elusive Rosser's sac spider was last seen. Now a colony has been discovered at Chippenham Fen, a nature reserve in Cambridgeshire.

Only known from 2 sites
The Rosser's sac spider, or Clubiona rosserae, to give it its scientific name, is incredibly rare. The only other place in Britain where it has ever been found is at Lakenheath Fen in Suffolk. It was first discovered in the early 1950's but, despite intensive searching in recent years, conducted by the British Arachnological Society and Buglife, the only charity in Europe that exists to promote the conservation of invertebrates, it hadn't been seen since 2000. Fears were growing that the spider had died out in the UK.

The Rosser's sac spider, which is light brown in colour, was spotted in September by spider enthusiast Ian Dawson. A further search in mid-October revealed a colony of ten individuals.

10 spiders seen
"I was extremely surprised to find the first one and then when we went back a month later it was great to find more of them," he said. "If we've managed to find ten of them, I think there must be quite a sizeable population of Rosser's at that particular site."

The Rosser's sac spider is particularly choosy about where it lives. It prefers wetland areas, the kind of habitat which has been consistently destroyed by the draining of the fens and changing farming methods since the Second World War.

Globally endangered
Buglife Chief Executive Matt Shardlow said: "This spider is globally endangered. It's fantastic that it's still creeping around in the British countryside and we're ecstatic that people can now see what it looks like for the first time in history. If we want future generations to be able to see the live animal, we will need to take great care of the tiny remaining fragments of wild wetlands in this country and reinstate large areas of lost fen."

Mike Taylor of Natural England, which manages the Chippenham reserve, said: "Rosser's sac spiders spend their days hidden in tubular silken retreats, often in a folded leaf, a bit like a sleeping bag. It's a member of the clubionid family of spiders who like to hunt their prey rather than catch them in a web. We were delighted that they have been spotted recently."

The first photographs of a live Rosser's sac spiders, both a male with large palps and a female, were taken by Peter Harvey, who took part in the second survey. "We were so pleased to find it in such good numbers," he said.