A hermit crab can carry its shell house wherever it goes. While studying hermit crabs, I learned that snail shells make good homes for crabs, but not perfect ones. For one thing, snail shells do not completely protect hermit crabs from their enemy, the octopus. Sea anemones fasten onto the hermit s shell and live there as in the picture above. The anemones help protect the hermit crabs.
Anemones have stinging cells in their tentacles that can hurt an attacking octopus.
I found some hermit crabs with lots of sea anemones on their shells and other hermit crabs with only one or two. Also, some hermits had sea anemones stuck close to the opening of the shell, and some had sea anemones stuck farther back on the shell. Every morning, I checked the aquarium to see if the octopus had eaten a crab during the night. I did this experiment 10 different times. In eight out of 10 tries, the crab with three anemones on its shell lived longer than crabs with one or no anemones.