Hermit crab predator evasion behaviour
On the rocky beach betwen Staithes and Port Mulgrave in North Yorkshire there are rockpools with large colonies of periwinkles. Walking towards them, I spotted sudden movement at my approach: shells rolling off the sides of the rockpool into the mass of periwinkles in the bottom of the pool. After a few minutes of still observation out came eyes, feelers and legs, and the cascading shells turned out to be hermit crabs, which then carried on about their business.
Remind me to tell you about my recent pelican observations at some point.