How Well Hermit Crabs See and Hear

[Crabby Abby]

Reply by eNature's Ask an Expert:http://www.enature.com/expert/expert_sh ... 16069Crabs in general can see pretty well, but they don't see quite the way we do. As arthropods, they have compound eyes similar to those of insects, made up of multiple, light-sensitive units called ommatidia. Crab eyes differ from insect eyes primarily by being mounted on mobile stalks, allowing a much wider field of vision and binocular vision. Hermit crabs, however, being primarily nocturnal, have ommatidia that are organized to maximize light detection at the expense of visual acuity and they combine to produce a single image. That is, hermit crabs see well enough in the dark to get around, and they see single but not very sharp images. Crabs (including hermit crabs) also hear pretty well, but again, not as we do. Their shells, and especially their antennae, are covered with microscopic hairs, some of which sense vibrations (others are used for "smelling") and send a message to the nervous system. However, they seem to be much more responsive to shock waves than to sound waves, so perhaps they're feeling more than hearing. Sometimes it's a fine line distinguishing senses.