Not so ‘incy wincy’ spider makes incredible comeback on RSPB nature reserves

• The Fen Raft Spider was previously threatened with extinction, but has since made an incredible comeback following successful conservation efforts by the RSPB and partners 

• The female spiders are known for their creation of nursery webs, spanning up to the size of a regular pizza, where they safely house their young 

• Now is the perfect time to see these incredible spiders, including the RSPB Mid Yare reserves on the Norfolk Broads, with the reserve teams predicting a good year for sightings 

Fen Raft Spiders, one of the rarest spider species in the UK, is anticipated to have their best year on record at RSPB nature reserves. Previously threatened with extinction, population numbers on the Norfolk Broads are steadily increasing thanks to conservation efforts. 

Adult female Fen Raft Spiders grow up to the size of your palm – but, arachnophobes will be pleased to know, are harmless to humans. They have a striking appearance, with distinctive white or cream stripes running along the side of the abdomen. The spider is semi-aquatic and an ambush predator where they 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. 

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. 

The RSPB Mid Yare nature reserves site manager, Tim Strudwick, talks more of the spider’s success across Norfolk: “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!” 

Thanks to a successful translocation partnership project, the species population is thriving. A collaboration between several conservation partners increased the number of sustainable populations from three to 12, by translocating spiders to suitable areas of restored habitat. 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. 

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. 

As Tim continues to explain: “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 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 and 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”.