Four Hundred Fen Raft Spiders (Dolomedes plantarius) Released in the UK

Zookeepers at Chessington World of Adventures (CWoA) park have released 400 baby fen raft spiders (Dolomedes plantarius) in the wilds in the UK to protect the endangered species from extinction.

The organization has been rewarded with a gold medal at the annual BIAZA awards for its conservation efforts.

Fen raft spiders are the largest of the UK’s 660 spider species and can grow to have a total leg span of almost 8 centimeters. They have brown or black bodies with white or cream stripes along the sides. These spiders are found in fens and other wetlands, and can move across the water surface due to their hairy legs. They eat pond skaters, small spiders, and dragonfly larvae. They can also kill tadpoles and small fish to consume.

Female fen raft spiders are known as caring mothers as they build an egg sac for their offspring. The mother spiders then routinely dip into water to keep the sac moist. The mother spiders also spin a nursery web that forms a silk tent over the water for spiderlings, and guard these webs for a couple of days.

The Fen raft spiders are listed as an endangered species in the UK because of their declining populations in the UK. There are only three known populations of fen raft spiders in the UK – at Pant-y-Sais Fen and Crymlyn Bog near Swansea, at Redgrave and Lopham Fen in Suffolk, and at Pevensey levels in East Sussex.

The credit for discovering the fen raft spider in the UK goes to famous arachnologist Eric Duffey who had found them at Redgrave and Lopham Fen in 1956. Later in 1988, a second population was discovered in the UK at Pevensey Levels in East Sussex. Then in 2003, naturalist Mike Clark discovered a third population on an abandoned canal near Swansea, South Wales.

Since 2011, zookeepers at CWoA have been working on a conservation program to protect fen raft spiders from getting extinct in the UK. The staff is rearing baby spiders in test tubes, and as these spiders grow adult, they are released in the wilds. The hard work of the CWoA staff has resulted in almost doubling of fen raft’s population in the country.