People with arachnophobia might want to steer clear of a Norfolk nature reserve, because spiders there which can grow to the size of a palm are thriving.

The fen raft spider, which can have a leg span of up to 8cm, was once commonplace on the waterways, but its numbers dwindled due to the loss of wetland habitats.

But a project to re-establish the water-walking giants, which saw thousands of spiderlings introduced at Strumpshaw Fen and Thurne Marshes in Norfolk and at Castle Marshes and Carlton & Oulton Marshes in Suffolk, has been hailed a huge success.

At RSPB land close to Strumpshaw Fen, near Brundall, where the spiders were first released in 2012, more than 480 nursery webs have been counted this season (July to October), compared with 184 in 2014.

Tim Strudwick, RSPB site manager at Strumpshaw Fen, said: 'The spiders are doing so well due to the excellent condition of the habitat and our management of the grazing marshes is maintaining ideal conditions for them. They have exactly the right vegetation mix along the ditches to support their nursery webs and the richness of invertebrate prey that the spiders need. It is great to see the spiders are responding by extending their range into new ditches.'

The fen raft spider is a striking creature with a dark body and cream stripes down the side; they are very large and females can sometimes reach up to the size of the palm of a hand.

Up until 2010 there were only three known populations in the UK, leaving the species very vulnerable and at real risk of extinction.

• What do you think? Write, with full contact details, to Letters Editor, Prospect House, Rouen Road, Norwich NR1 1RE or email