You can witness this when you dive or scuba here. Peter Fuller

In the Port Philip Bay near the coast of Melbourne, hundreds of thousands of giant spider crabs migrate to the shallows to moult. Using their safety in numbers to protect them while their new shells harden.

The crabs grow up to 16 centimetres in size and pile up to ten crabs at a time when they’re migrating. You can watch this happen when you dive in the bay, but even when you’re only snorkelling.

The migration of giant spider crabs, Port Philip Bay, Australia