Thousands of endangered spiders have been released into a Suffolk nature reserve this week as part of a conservation scheme to stem their decline in the UK.

The ecologist Helen Smith, working with the government body Natural England, has hand-reared the 3,000 baby fen raft spiders in her own kitchen. She said: "They are all lined up in individual test tubes and I've had to personally feed them flies since the spring – which you can imagine is very, very time consuming for that number of spiders."

Test tubes containing spiderlings. Photograph: Natural England/PA

The fen raft spiders are one of only two British spiders that are fully protected by law. They can grow to 5cm in length and are noted for their distinctive markings and elaborate courtship rituals. The spiders are named after their ability to float on water in the fens and wetlands where they live – thanks to their hairy legs.

The baby spiders (or spiderlings) are cross-breeds whose parents come from two tiny populations that remain in Sussex and Suffolk. As a result the new population will have greater genetic diversity than either parent population. Pete Brotherton, head of biodiversity for Natural England, said: "Numbers of fen raft spider have dwindled to perilously low levels in England – isolated to a few remaining pockets of habitat, it would be difficult for the remaining populations to recover on their own."

A programme of reintroduction has been underway for the last five years and the release of the fen raft spiders into the wild, supported by the BBC Wildlife Fund, marks the culmination of this work. Smith said: "It's very exciting and lots of people as well as me have been working towards this so hopefully it will be a happy ending for the fen raft spider."

But Smith said many of the spiderlings would not make it to adulthood. "They are delicate beings and face a lot of threats in the wetlands. But it won't be till next summer when we know how many survived so I'll have to hold my breath through the winter."

• This piece was amended on 22nd October 2010. We originally referred to the spiderlings as being a "hybrid species". This is incorrect and has been changed.