One of Britain’s rarest and most spectacular spiders has been introduced to the Norfolk Broads after an intensive captive breeding programme.
A thousand hand-reared fen raft baby spiders or spiderlings have been released on the RSPB’s Mid-Yare reserve in an effort to generate new populations of this vulnerable species in Norfolk, where they are now restricted to a single site.
The fen raft spider, (Dolomedes plantarius) is Britain’s biggest spider and can grow to the size of a woman’s palm with a body length of 23mm. It can literally walk on water to catch its prey but owing to deterioration and loss of wetland habitats, its population has suffered. It is listed as Vulnerable on the IUCN’s Red List of Threatened Species and as Threatened in the UK Red Data Book.
The fen raft spider is only found on three wetland sites in the UK - Redgrave and Lopham Fen National Nature Reserve in Norfolk where it was first discovered in Britain in1956, the Pevensey Levels in Southern England and in South Wales.
The release of the baby spiders were watched by their foster parents, mainly staff from zoos, who have patiently reared them in individual test-tubes over the summer. The spiderlings have been bred from the wild population at Redgrave and Lopham Fen Reserve.
Ecologist Dr Helen Smith, who co-ordinates the Fen Raft Spider Species Recovery programme for Natural England, devised the test tube rearing techniques with the John Innes Centre in Norwich. She has reared 5,000 spiderlings in her own kitchen over the last three years.
“I think everyone who does captive rearing gets very attached to them,” she said. “The baby spiders each have their own test-tube to avoid them eating each other so you have to devote yourself to feeding them for three months. We achieve survival rates of around 90% over this period, when survival in the wild would be very low.
“The Mid Yare reserve is a very good habitat and the spiders will be able to spread easily from the release site. It’s very exciting to be able to establish a new population in the heart of the Broads.”
Tim Strudwick, RSPB Site Manager, said "We are delighted to be able to provide a new home for fen raft spiders. The RSPB staff and volunteers have worked hard for many years to get the grazing marsh habitat into good condition for all kinds of wildlife and seeing ‘lost’ species return is the best reward.”
Between 2010 and 2012 nearly 12,000 spiderlings will have been released to the wild to establish new populations in Norfolk and Suffolk. At Suffolk Wildlife Trust’s reserve at Castle Marshes near Lowestoft they have been breeding successfully this year, producing an estimated 50 nursery webs. The aim of the programme is to secure the future of this species in the UK by increasing the number of populations from three to 12 by 2020.
The Fen Raft Spider Translocation Programme is funded by Natural England England, the Broads Authority, the BBC Wildlife Fund and volunteers. Other partners are the Suffolk, Sussex and Norfolk Wildlife Trusts, RSPB, the University of Nottingham, Buglife and the British Arachnological Society.
For more information about the programme visit: www.dolomedes.org.uk
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