Make space for massive spiders

“I am one of those people if a spider ran across the floor, I would take my feet off the floor and jump up onto the chair, says Tim Strudwick, the reserves manager for the RSPB in the mid Yare valley in Norfolk.   
“I just have this awful instinct, it is completely illogical. But I am getting better at it.” 
 
Thankfully for Tim, his phobia of spiders is mainly confined to those found in his house. He has much more time for the fen raft spider, the UK’s biggest spider, which now has recolonised several RSPB reserves he manages along the River Yare.

Until 2010, three isolated populations of fen raft spider remained in the UK, leaving its future hanging by a thread. Tim said: “Those three original locations were and still are incredibly threatened, from things such as drought, sea level rise, tidal surges – anything like that could literally wipe them out.” 

But this wasn’t always the case. Historically the spider was much more widespread and was probably in the Yare Valley hundreds of years ago. But as people drained the landscape and fragmented the wetlands, populations vanished and a top predator disappeared from ecosystems.  

Tim said: “It was probably on its last legs even in the 19th Century before becoming very close to extinction in the 20th Century – but then the decision was made to take action just in the nick of time.”  

A breakthrough project was set up in 2010 with lots of partners, including the British Arachnological Society, Natural England, the British and Irish Association of Zoos and Aquariums and the University of East Anglia. They devoted time to learning more about the spiders and trialled breeding them in captivity. The team also looked for suitable sites for possible translocations, with the Yare Valley chosen as an ideal spot because of its size and rich tapestry of wetlands habitats. 

The first spiders were released in 2012 on RSPB land at Cantley Marshes. The spiders soon made themselves at home in the grazing marsh and ditches and numbers rapidly increased. By 2020 they had reached another RSPB nature reserve close by, Strumpshaw Fen.  

Tim said: “The first record at Strumpshaw was a visitor who spotted a big female with her egg sack walking across the visitor path. He took a photograph and asked us “what’s this?” 

Over the last decade Tim and the team have spent many hours monitoring and learning about the spiders, finding out key information which may help them further increase in number.   

Tim said: “At the start there was uncertainty about what habitats they liked and what we’ve learnt is that the habitats they do best in are not the habitats they had been mainly confined to.   

“It’s very similar to red kites – when I was a kid and keen bird watcher you could only see them in central Wales and they weren’t doing that well there. The only reason they were there is because they had been wiped out in the rest of the country by human activity. But now they’re doing really well as they’ve been reintroduced into other areas.  

“This is the same – we’ve seen the fen raft spider does really well in grazing marshes with ditches with a lot of vegetation in, this is the area they seem to thrive in.” He added: “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.” 

With their breeding female numbers now reaching around 10,000 on Tim’s patch, you’d think the UK’s biggest spider would be easy to spot. But as they’ve now spread over a large area the best way to see them is when the females create a nursery for their young.  

Tim said: “The female lays her eggs into a sack and when the young come out of that sack about three weeks later, they form a nursery in the water plants – you can see it just above the water surface. So this is what we’re counting, once you see one and get your eye in you start seeing them everywhere because they are quite a unique thing.” 

Tim added: “They catch the dew and if you come on a morning, a sunny morning, the light goes through them, and they glow – you can see them with the naked eye 20m or so away.” 

With population increasing, the hope is that the spider will continue to spread further along the Yare. Tim said: “We just don’t know how far they are going to spread and that’s what’s exciting, seeing which bits of habitat they take over next.” With the spiders spreading, there is more chance of visitors spotting them and the team hope they will soon be able to show visitors where to look for them.  

Tim said: “We really do want people to see them now, it is a great story to tell. Go back ten years or more and there hadn’t been many translocations of invertebrates and most of them had been failures, or not had a great success rate. So it’s great to see one that is really succeeding.”