Thousands of giant spiders that can grow to the size of a human hand are thriving in the UK, thanks to a successful breeding programme from Chester zoo. The fen raft spider is a harmless arachnid that plays a vital role in aquatic ecosystems, but 15 years ago was on the brink of extinction because of habitat loss. Chester zoo worked with the RSPB to raise hundreds of baby spiders, keeping them separate in test tubes so that they did not eat one another. The spiders were hand-fed with tweezers in the zoo’s bio-secure breeding facility until they were big enough to be released into the wild. This year, the spiders have had their best mating season on record, Chester zoo said, with the RSPB estimating that there are 10,000 breeding females across the UK. According to London zoo, the stretched-out leg span of a fen raft spider is typically 65-70mm – roughly the width of a human palm or the length of a newborn rat. The zoo was also involved in the breeding programme, along with other members of BIAZA, the British and Irish Association of Zoos and Aquariums. The spiders were hand-reared between 2011 and 2013, and later released into the wild. Chester zoo said it had helped to release “thousands” 10 years ago, adding “you can’t miss them, they grow to be the size of your hand!” “We’re super proud to be part of this conservation breeding rescue programme, working alongside our friends at the RSPB to prevent the extinction of the fen raft spider,” the zoo said in a post on X. Also known as the great raft spider, the semi-aquatic arachnids have a chocolate-brown body with cream stripes along the side and are able to walk on water. They live in unpolluted fens and marshes. The first fen raft spider population in the UK was identified in 1956 by the arachnologist Dr Eric Duffey, at the source of the River Waveney in East Anglia. “Of course, there is also nothing to fear from increased numbers of spiders,” Dave Clarke, who heads up London zoo’s Friendly Spider Programme, wrote in a blog post. “This is a huge conservation success, both for the spiders and the wider habitat restoration driving the success. And more natural bio-controls out there (even if this species is never coming into human areas) are only a good thing.”