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A milestone for fen raft spider project

Monday 9th July 2012

The first Raft spider nursery web found at Castle MarshesThe first Raft spider nursery web found at Castle Marshes

A collaboration between Suffolk and Sussex Wildlife Trusts is helping to save one of Britain’s rarest spiders.

Following the introduction of hundreds of baby Fen Raft Spiders to Suffolk Wildlife Trust’s Castle Marshes nature reserve in 2010, the first evidence of successful breeding has just been recorded. The Trust’s Suffolk Broads reserve warden Matt Gooch commented: “Spiders appear to have readily taken to Castle Marshes evidenced by the exciting appearance of the first spider nursery built by brooding females this week.”

The spiderlings were reared in captivity in project leader Dr Helen Smith’s kitchen for the first three months of their lives. Each spider lived in an individual test tube and had to be fed on tiny fruit flies. In the wild, very few of the tiny spiderlings survive but over 90% of them survive when they are reared in captivity. This provides large numbers not only for establishing new populations but also for reinforcing the source populations.

Helen says: “This is a really exciting day and a major milestone in our work to establish new populations of this beautiful but extremely rare spider. Although it’s still early days for assessing whether the new population in Suffolk will thrive, this is the best possible indication that this is a suitable new home for the spiders.”

Longstanding volunteer George Batchelor who has been involved with the project from the beginning said: “The adult spiders that have now bred and produced young on Castle Marshes are the same little spiderlings that Helen nurtured in her kitchen two years ago. When we released these tiny little things from their test tubes, the weather turned very cold shortly afterward and I feared for their future. The survival and success of these Raft Spiders in the numbers we have seen, proves the habitat of our water soldier filled dykes is ideal; the female even chose a water soldier plant to hatch her young brood! We are so proud to have these spiders on the reserve and monitoring will now become a priority.”

The spiders take two years to mature and so this is the first season when breeding could be expected. On 6 July, the first nursery web – a large silk ‘tent’ containing hundreds of tiny baby spiders – was found in vegetation above the water at the edge of one of the site’s many ditches. Guarded by their mother, the spiderlings are expected to leave the web after about a week to begin life on their own.

This species is known from only two sites in England – on Suffolk Wildlife Trust’s Redgrave & Lopham Fen nature reserve and on the Pevensey Levels in Sussex. The spiderlings introduced to Castle Marshes (which lies on the same river as Redgrave & Lopham Fen), came from both of these sites – those from Sussex coming from Sussex Wildlife Trust’s Pevensey Marshes nature reserve . Alice Parfitt, Pevensey Marshes Reserves Officer commented: “Given the rarity of this extraordinary spider, and the strength of the population on the nature reserve, it was a straightforward decision to support their introduction to Castle Marshes; we’re delighted to now hear they’re thriving.’

The programme to establish new populations of the spiders is part of Natural England’s Species Recovery Programme, with many organisations working together to make it a success. Suffolk and Sussex Wildlife Trusts, their nature reserves and their volunteers, are playing a major role, with funding from Natural England, The BBC Wildlife Fund and the Broads Authority. Eleven of Britain’s Zoos are now also playing a vital role in the work, acting as foster parents for the tiny spiderlings.

A second introduction, to Suffolk Wildlife Trust’s Carlton Marshes nature reserve, is already underway and it is hoped that introductions will soon begin on an RSPB nature reserve.

David Heaver of Natural England says: “This partnership has worked hard to reverse the fortunes of one of our most endangered and iconic wetland species. Today’s news is an important step towards our goal of ensuring that these spiders are no longer at risk of extinction, and because some of these rich wetland sites have such good accessibility the spiders can be seen and enjoyed by many more people.”

Tagged with: Castle Marshes, Fen raft spider