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Fen raft spider

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The fen raft spider is one of Europe's largest and rarest aquatic spiders and was only discovered living in Wales in 2003.

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Last updated: 05 April 2011

Up until a few years ago, this species was only found in two locations in the whole of Britain and they were both in eastern England. Fen raft spiders are also protected under the Wildlife and Countryside Act of 1981.

These semi-aquatic spiders can grow up to 7cm in length and are a rich chocolate brown colour with a distinctive cream stripe along the sides of their body.

Raft spiders prefer slow moving water and live in fens and marshes in lowland areas and require warm, sunny conditions.

The spider feeds on small fish such as sticklebacks and tadpoles and other aquatic invertebrates.

When prey is located they can actually run across the surface of the water to attack and can even hunt underwater by running up and down sedge reeds.

The short, velvety, water-repelling hairs covering the body and legs then allow these large spiders to do the seemingly impossible - walk on water like pond skaters.

The spiders can actually perch on the water surface using the surface tension of the water to keep themselves afloat hence the name 'raft spider'.

The best time to spot them is when the females are raising their young as the large nursery webs, full of baby spiders can be easily spotted on long, stiff reeds.

Raft spiders were only discovered living in Wales in 2003 in the Tennant Canal at Pant y Sais Fen but have probably been here for at least 100 years.

Pant y Sais Fen is a limb of Crymlyn Bog and translates as 'The Englishman's Hollow' and is a nature reserve alongside the village of Jersey Marine in Neath.


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