by Ruth Brooker
One of Britain’s rarest spiders is to be re-introduced to the Norfolk Broads this week, after a successful captive breeding programme.
The fen raft spider is the largest spider in the UK; when fully grown its leg span can measure up to 8cm and it has a body length of 23mm. It was first discovered living in the wetlands of East Anglia in 1956. This spider doesn’t spin webs to catch its prey; it walks on water and hunts for food that is either on the surface of the water or swimming underneath. It is big enough to catch small fish and newts.
Unfortunately, the fen raft spider is listed as vulnerable on the IUCN’s Red List of Threatened Species. It has also been categorised as needing special help if it is to recover and thrive again in England. They are currently only found on three wetland sites in the UK; at Norfolk, Southern England and South Wales.
Wildlife organisations including Natural England and the Broads Authority, are working together on the Fen Raft Spider Translocation Programme. One thousand hand-reared baby spiders will be released this week on to the RSPB’s Mid-Yare Reserve in an effort to generate new populations in Norfolk.
The baby spiders have been patiently reared – mostly by staff from zoos – in individual test tubes over the summer. Dr Helen Smith, who is co-ordinating the programme, devised the test-tube rearing techniques and has personally hand-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. 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.”
Between 2010 and 2012, nearly 12,000 baby spiders will have been released to the wild to establish new populations in Norfolk and Suffolk. At the Castle Marshes Reserve near Lowestoft, they have bred successfully this year and produced an estimated 50 nursery webs. The aim of the programme is to secure the future of this species by increasing the populations from three to 12, by 2020.
The Translocation Programme is funded by Natural 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.