Did you know that crabs migrate? Unlike birds that fly south for the winter to avoid the frigid cold, giant spider crabs head to the shallow waters of Australia’s southern coast in pursuit of warmth. Each year, hundreds of thousands of crabs migrate, and one scientist was lucky enough to capture video of a giant horde of spider crabs as they gathered in Port Phillip Bay near Melbourne. Crowding together like this is an odd behavior that scientists don’t completely understand, but it is quite a spectacle to behold – check out a video after the jump.

Australian aquatic scientist Sheree Marris, a documentary film producer and former winner of three Young Australian of the Year awards, was exploring just off the coast when she came upon a mass of the giant spider crabs that she described as several hundreds of meters long. With the crabs stacked up to 10 individuals deep, it’s impossible to know how many crabs were present. Each crab can measure up to 12 feet from claw to claw, giving them greatest leg span of any arthropod on the planet.

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The reason for the giant spider crabs gathering together en masse is something scientists don’t completely understand. The prevailing theory, though, is that they cluster for protection during the molting season, when they become more vulnerable to predators after shedding their hard outer shells. Certainly, a crab that strays from the crowd would be easily picked off by a dogfish or a sea turtle. An alternative theory suggests the behavior may be related to mating.

Regardless of the reason for the giant spider crab mob, Marris hopes her video will help raise awareness of the diversity of marine animals off Australia’s coast, an area where many people have misconceptions about the nature of sea life. “Who would have thought something like this, that is so spectacular, could be happening in Australia on the southern shore?” she said.

Via BBC

Images via Sheree Marris