Spiders the size of a human palm make a comeback in the UK

One of Britain’s largest spiders, which can grow as big as a human palm, is making a comeback, with conservationists expecting a bumper breeding season.
Female fen raft spiders, which can measure 7cm across, have been known to catch small fish and tadpoles. They are, arachnophobes will be pleased to hear, harmless to humans.
This year they are thought to be on course to produce record numbers of spiderlings, with an estimated 3,750 females laying eggs.
Before 2010, only three isolated populations were known in the UK — in East Anglia, Sussex and south Wales — leaving the future of the species hanging by a thread.
In 2012, the spiders were introduced to four new sites in the Norfolk and Suffolk Broads, including at the RSPB’s Mid Yare nature reserves. Grazing marshes were restored to provide suitable habitats, including at Strumpshaw Fen and Buckenham and Cantley marshes.
The RSPB said it had created conditions for females to construct the large “nursery webs” they use to raise their young. Tim Strudwick, reserves manager for the RSPB in the Mid Yare Valley in Norfolk, said now was a perfect time to spot one.
“The spiders are only seen in the grazing marsh ditches and are fairly shy, but are easier to see from June to September,” he said. “Walking along the meadow trail gives visitors at Strumpshaw Fen the best chance of sightings of the mature females and their glistening nursery webs.”
Fen raft spiders are one of the largest varieties in Britain. Nursery web spiders, commonly found in gardens, measure about 5cm across. As with most spiders, the male is considerably smaller than the female. They are dark chocolate brown in colour, or greenish in juveniles, with a conspicuous white or cream stripe along each side.
Females will initially carry their silk-wrapped eggs in their mouths for three weeks, until the spiderlings start to appear. The mother will then spin a silk nursery web, suspended above water and about 25cm in diameter.
Strudwick 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 play 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.”
He added: “We’ve seen that the fen raft spider does really well in grazing marshes, with ditches with a lot of vegetation — this is the area they seem to thrive in.
“A lot if it is down to food. They’re a generalist predator, taking a lot of different invertebrates, so if we have a lot of those around, like dragonflies and damselflies, that’s the sort of habitat they really like.”
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The spider is semiaquatic and an ambush predator, so actively hunts its prey instead of building webs to catch a meal. The legs of fen raft spiders are covered in tiny hairs that detect the slightest of vibrations on the water’s surface, which they run across to capture their quarry.
Their diet includes other spiders, damselflies, dragonfly larvae and pond-skaters. They will occasionally catch fish and tadpoles.
The RSPB said there was little chance of crossing paths with one in your home. “Found in only a handful of sites in England and south Wales, you won’t come across these eight-legged friends scuttling under your bed,” a spokeswoman said.
“In fact, until 2010 there were only three known populations in the UK, leaving the species very vulnerable.”
She added: “In terms of predators, fen raft spiders could possibly be eaten by toads, frogs and some species of bird.”