Stingray Ambushes Army Of Crabs | Blue Planet II | BBC Earth

Summary by Krater

An army of hundreds of thousands of spider crabs gathers in Australian waters near winter to molt simultaneously, offering safety in numbers despite the threat of stingrays.

From the video

Answers: Why do spider crabs gather in massive armies in Australian waters?

• spider crab aggregation
• crustacean molting
• marine predator avoidance
• Australian marine life

What it concludes

• hundreds of thousands of spider crabs gather to molt simultaneously for mutual protection.
• the crabs assemble in dense mounds nearly 100 meters long.
• stingrays are attracted to feed on newly molted, soft crabs during the gathering.
• the vast majority of crabs successfully escape and return to deep waters after molting.