If you think you see the beach moving, it’s not the heat nor last night’s excess of guaro messing with your mind. Daily, whole columns of seashells—little whelks and conchs of green and blue and russet—come marching down from the roots of the mangroves onto the sand.
Scavengers only an inch long, soldier crabs are born and grow up without protective shells. For self-preservation they move—“lock, stock, and abdomen,” says one writer—into empty seashells they find cast up on the beach. Although they grow, their seashell houses do not; thus whole battalions of crabs continually seek newer and larger quarters. When threatened, a soldier crab pulls back into its shell, totally blocking the entrance with one big claw.