A 50,000-strong swarm of spider crabs (Leptomithrax gaimardii) mate on the seabed of Melbourne's Port Phillip Bay, 25 May 2005, at the start of their breeding season. Scientists are baffled by the size of the enormous gathering which is scaring away all other sealife from the area in the four-metre-deep water near an undisclosed beach. (I may freak out if I see this happen here) :)