Chester Zoo Fen raft spider: How big are they as one of UK’s rarest spider species makes a comeback

Video shows a fen raft spider in the UK - with thousands of the species now in the country despite previously being threatened with extinction.

Posting the footage to X on April 9, Suffolk Wildlife Trust North East Reserves wrote: “Fen raft spiders starting to appear on the Dyke networks of the Lower Waveney Valley. This one was battling the wind even on this sheltered Dyke line”.

The RSPB say fen raft spiders, one of the rarest spider species in the UK, are on track to have their best year on record at their nature reserves, with population numbers on the Norfolk Broads steadily increasing thanks to conservation efforts.

In a post to X on October 30, Chester Zoo said: “Ten years ago we helped release thousands of giant spiders back into the UK. The fen raft spiders were bred right here at the zoo, and we’re super happy to report there’s now more than 10,000 breeding females… and they’ve just had the biggest mating season on record.”

How big are fen raft spiders?

Fen raft spiders are fairly large, the size of your palm, at 65-70mm typically. They have a mainly brown body with a beige coloured stripe down either side and speckled legs.

What do fen raft spiders eat?

Fen raft spiders eat insects, tadpoles and occasionally fish.

Do fen raft spiders pose a risk?

Fen raft spiders are completely harmless to humans.

What are the threats to fen raft spiders?

Fen raft spiders are listed as vulnerable on the IUCN red list of threatened species. London Zoo worked with Natural England to rear fen raft spiderlings into adults, which were then reintroduced back to the wild.