The great raft spider, Dolomedes plantarius, is a water-gliding giant that lives only in wetlands and can achieve a leg span of up to 3 inches.
Ten zoos across the country have joined in the effort to raise spiderlings hatched from eggs collected in one of only three wetland locations where the thick-legged creatures still survive.
“Most invertebrate groups don't receive a lot of conservation effort,” spider expert Helen Smith told the BBC.
But with funding from Nature England, the Broads Authority the BBC Wildlife Fund and volunteers, the first batch has been released at the Royal Society for the Protection of Birds’ Strumpshaw Fen reserve near Norwich.
The spiderlings are raised and fed individually in test tubes to keep them from eating their siblings and to increase their survival rate.
In the wild, they are a fairly benign predator, eating only common species that are not endangered, says Smith, who began raising the spiders in her kitchen before being joined by others in the conservation project.
The great raft is only being introduced into the most biodiverse habitats, such as those that have recovered from the effects of agricultural drainage that vastly altered the UK’s ecology during the 20th century.