Britain's biggest spider - the size of a man's hand - is surging in numbers, new research reveals.

While it may horrify arachnophobes, the huge growth in numbers of the Fen Raft Spider is a conservation success story.

The spider - which spins webs as big as pizzas (25cm) - was on the verge of extinction in the UK in 2010.

Then, the spider was restricted to just three sites in the UK in Suffolk and Sussex and just a handful of spiders remained. 

But thanks to a successful breeding campaign numbers are up to 3,750 breeding females at 12 sites in Norfolk alone. 

Efforts to improve the creatures habitat and damp weather this year are thought to have given the species a boost.

The RSPB Mid Yare nature reserves site manager, Tim Strudwick, said he was proud that the spider had recovered. 

He said: '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.'

Fen raft spiders have distinctive white or cream stripes running along the side of the abdomen. 

The spider is semi-aquatic and can run across the water’s surface to capture their prey. 

Their diet includes other spiders, damselflies, dragonfly larvae and pond skaters, and they will even catch fish and tadpoles. 

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.

He added that the spiders can be seen in another RSPB site in Norfolk, Strumpshaw Fen, adding: '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.'

RSPB ecologist, Jane Sears, was involved in Fen Raft Spider conservation said: '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.'