The fen raft spider (Dolomedes plantarius) is the largest spider species in the UK. It can grow to nearly the size of a mouse, uses its spiky leg hair to walk across water, and feasts on everything from insects and smaller spiders to tadpoles and fish. And, for the last two years, a UK zoo has been releasing hundred of the gargantuan spiders back into the wild.

While that may be terrifying news for arachnophobes, it’s great for the fen raft spider, which is an endangered species. National Geographic reports that the Chessington World of Adventures began breeding the spiders in captivity several years ago in hopes of eventually increasing its population in the wild. Over time, the zoo managed to release 400 spiderlings into the UK’s wetlands, where their population has nearly doubled.

According to The Telegraph, the fen raft spider thrives in watery environments, so you’re not likely to stumble upon one in your home. And, despite their size, they’re harmless to humans. In fact, they play an important role in their ecosystem; according to a Chessington World of Adventures press release, humans have done much more damage to the spiders by encroaching on their environment than the spiders have ever done to humans. 

Chessington World of Adventures recently won a gold certificate at the annual BIAZA Awards for their work with the fen raft spider release program. “The successful work on reintroducing the Fen Raft species is a great example of the good zoos can do in helping conserve endangered species in the wild,” Chessington supervisor Keith Russell explained. 

[h/t National Geographic]