Fen Raft Spiders, one of the UK’s rarest spider species, are anticipated to have their best year on record at RSPB nature reserves, thanks to conservation efforts.
Back in 2010, the future looked bleak for Fen Raft Spiders, with this wetland arachnid on the brink of extinction. But concerted conservation efforts have paid off and population numbers on the Norfolk Broads are steadily increasing.
Fen Raft Spiders are semi-aquatic spiders, named for their ability to run across the surface of the water to catch their prey, ‘floating’ like a raft. Many people also consider them strikingly beautiful, with their distinctive white or cream stripes running along the sides of their bodies.
But these remarkable spiders are struggling. So in a pioneering translocation project, conservation partners came together to reduce the risk of Fen Raft Spiders becoming extinct.
Working together, the RSPB, the Suffolk and Sussex Wildlife Trusts, Natural England, the Broads Authority, and the British Arachnological Society, together with funders and supporters, established new sustainable spider populations in the Norfolk Broads.
This was achieved by introducing spiders to four sites on the Norfolk and Suffolk Broads, including the RSPB Mid Yare reserves. Sensitive restoration of grazing marshes by reserve teams across the RSPB Mid Yare reserves, which includes Strumpshaw Fen, Buckenham Marshes and Cantley Marshes, have created the perfect vegetation mix for nursery webs and provide plenty of prey for the spiders.
In total, the number of sustainable Fen Raft Spider populations have increased from three to 12, and all the signs so far are that they are thriving.
The most recent survey estimates the total number of female spiders is now into the thousands, with potentially 3,750 individuals – an impressive figure for a species that was previously at risk of extinction in just 2010.
Whilst the species remains Vulnerable and listed as a Priority Species, the annual spider surveys take place in September at these reserves and hope to be another successful breeding year.
Adult female Fen Raft Spiders grow up to the size of your palm – but, arachnophobes will be pleased to know, are harmless to humans.
The females demonstrate incredible parenting skills by building an egg sac to carry their babies around for three weeks, carefully dipping it into water every few hours to prevent the sac from drying out. The female does not eat during this period and eventually spins a silk nursery web just before her young are ready to hatch. The nursery web is then suspended above water and can span up to the size of a regular pizza (or 25cm across) and is fiercely guarded by the protective mother.
Fen Raft Spiders actively hunt their prey instead of building webs to catch their next meal. Their legs are covered in tiny hairs that detect the slightest of vibrations on the water’s surface which they can run across to capture their prey. Their diet includes other spiders, damselflies, dragonfly larvae and pond skaters, and they will even catch fish and tadpoles.
RSPB Mid Yare nature reserves site manager, Tim Strudwick, explains: “The Fen Raft Spider is one of the UK’s rarest invertebrates and we are proud of the role our reserves and teams have played in its recovery. These spiders have an important role in maintaining the rich aquatic diversity found in the grazing ditches on our reserves. The females are impressive in size, but also beautiful – they are truly special to see!”
The success of this project demonstrates how vital conservation efforts are in species restoration. RSPB ecologist, Jane Sears, was involved in the Fen Raft Spider partnership adds: “The RSPB has played an important role in the reintroduction of these spiders and means we must continue to restore, manage and protect the wetland habitats where the Fen Raft Spider thrives to ensure the future of not just this species, but many others too”.
The RSPB's Mid Yare Valley nature reserves includes Strumpshaw Fen in the Norfolk Broads. Nature reserves site manager Tim Strudwick explains how to look for Fen Raft Spiders:
“The spiders are only seen in the grazing marsh ditches and are fairly shy but are easier to see from June to September. Walking along the meadow trail gives visitors at Strumpshaw Fen the best chance of sightings of the mature females and their glistening nursery webs, so now is the perfect time to make a trip to the reserve”.
The RSPB's Mid Yare Valley nature reserves protect a mosaic of wetland habitats, and the RSPB is continuing to enhance the habitat and improve water quality in the River Yare.
