The Japanese Spider Crab is the biggest arthropod on Earth--their legs are believed to grow up to 12 feet long. So for now, we'll have to make due with the 5 foot long Crabzilla), one of the largest known crabs in the planet. According to the BBC, Crabzilla will be the biggest crab ever seen in Britain when it's brought on show at Birmingham's National Sea Life Centre. The crabs are commonly found in the Pacific in 1,000 ft (300m) deep waters but have been known to live deeper. It is rumoured these crabs can grow as big as four metres, big enough to straddle a car.