Arachnophobics beware...scientists have found the world's biggest ever fossilised spider. The amazing discovery had a leg span of more than five inches and was found encased in volcanic ash at the bottom of what used to be a lake in Mongolia.

The specimen lived 155 million years ago and was a female golden orb-weaver spider (dubbed Nephila jurassica). The Nephila species can still be found today in various tropical locations, and are around the same size as this prehistoric version.

Professor Paul Selden from the University of Kansas unearthed the crusty creepy-crawly. He believes the find is extremely significant.

He said: "It's very rare to find fossilised spiders because their bodies are soft so they normally decompose very easily. But there are certain beds - like where this specimen was found - that are made of a very fine volcanic ash which preserves all the details very well."

Most prehistoric spiders are found in amber, which only survives from the crustaceous period and began around 20 million years later.