With a leg span of more than 3 inches, the great raft spider Dolomedes plantarius is one of Britain's largest arachnids.
Scientists said people should not be concerned about plans to release spiders into the wild, as they only live in wetlands and very few survive there currently.
A number of British zoos and wildlife facilities have been raising baby raft spiders, so named for their ability to glide across the surface of lakes and rivers in search of prey.
Ecologist Helen Smith said the project's intention is not to flood the wetlands with giant spiders, merely to repair the damage already done through habitat loss from agricultural drainage that dramatically altered the landscape in the 20th century.
"Most invertebrate groups don't receive a lot of conservation effort," Smith told the BBC. "The ones that tend to receive the attention are the big and spectacular ones... this is very much the case with [great raft spiders].
"They're big, they're beautiful and they have to fly the flag for other species."