Tens of thousands of giant spider crabs captured migrating in Australia

Tens of thousands of giant spider crabs were captured on video migrating in Port Phillip Bay, Australia. The crab swarm happens every year as the water cools and the creatures "come into the shallows to molt," according to AccuWeather.

The crabs' new skeletons takes time to harden, during which they are vulnerable to predators. Giant spider crabs can be over 3 feet long and live up to 100 years.