How do hermit crabs pick the very best shells?

In the rocky tide pools of Northern California, hermit crabs are constantly looking to upgrade the homes on their backs. They might find a slightly larger shell that fits their needs, a new shell might be safer than their old one, or a black turban snail shell, grown over decades from the water’s calcium carbonate minerals, might become available.

This KQED Deep Look episode observes how These Feisty Hermit Crabs Brawl Over Snail Shells.

And in any of these situations, the hermit crab’s primary skill is on display: They are scavengers. That’s essential for their ecosystem because they help keep tide pools clean.

From Oceanbites, a University of Rhode Island Graduate School of Oceanography science communication site:

Previously, hermit crabs were thought to be primarily deposit detritivores, which means that they were filtering the sediment around them, looking for small pieces of food to eat. Now, we can think about hermit crabs as a larger contributor to the whole tide pool food web. Animals that eat other dead animals are important to nutrient cycling. They ensure that the nutrients that the dead animal contained don’t get washed away with the tides. Hermit crabs are more important to the ecosystem than we knew!

Deep Look also illuminates what’s going on inside a hermit crab’s shell:

While the front of their body is covered in stiff armor, their elongated back half is soft. It curves to match the shell’s spiral shape. At the very end of its body, deep inside the shell, modified legs called uropods grab on, like the arms of an anchor.

Watch these related crab and shell videos next:
• Hermit crabs line up to exchange their shells
• Pagurus Bernhardus hermit crabs change their shells
• Pharaoh cuttlefish expertly mimic hermit crabs

Plus: More videos from Deep Look.