This is a case of squatters in others' houses called hermit crabs. They are called such because they inhabit abandoned sea shells. They are crustaceans with ten feet (decapods) and have very soft and vulnerable body. So when disturbed they immediately retract inside the shell for protection. They also grow and increase in size, so growth allows them to abandon the old shell and find another bigger one. What is amazing about them is the drama during the time of transfer to bigger shells. When a new bigger shell is found, many of them gather around it or queue from biggest to smallest. As soon as the largest crab moves into the new shell, the 2nd largest moves into the newly vacated shell, making its old house available for the size next to it, and so on. It would be nice to document that event, how i wish to find them doing that, but i didn't.
Most of you will remember my post a few weeks ago about my trip to an island at the south of the country, where i saw a big Crinum lily. I found a lot of these creatures resting the whole day in leaf axils of that big white crinum lily. I disturbed their silence to take some photos. At high tide in the afternoon, they quickly crawled out to the water. I just don't know if it is the water or the absence of sunlight which triggered them to leave the sanctuary of the crinum lily.
This is the white big Crinum lily
a lot of the hermit crabs with different shapes and types of shells converged inside the leaf axils
They normally stopp when disturbed or touched, retract and hide inside their shell
This one, though reluctant, still obliged to pose. Take note of the already worn out shell, maybe it has been home already to many generation of inhabitants.