Why do hermit crabs chirp?

The hermit crabs of Ecuador region do chirp more than that of Caribbean species. Chirping is called as stridulation or making a shrill noise. Zoologists say that this noise is expressed when a body part is rubbed over another or on the shell by the crab. Chirping is mostly considered as a means of communication to everyone. In various other animals stridulation is done for breeding, territorial defense and disturbed mechanisms. The crab which is making noise can transmit those vibrations to our fingers when we touch a stridulating crab.

No one is clear about the reason for the chirping of Hermit crab. There was an experiment conducted by a nature lover to observe the behavior of a crab called ‘Slater’ which was in molting posture. This Slater was an Equadorian. Few crabs were placed in isolation and a lid was kept on the crab container. When the person raised the lid, the crab started chirping. When the lid was closed the chirping stopped. A crab was noticed to be performing molting at that period of time. The other crabs which were in pre-molting condition were removed and again the same procedure was repeated. When the lid was opened, again the molting crab made noises and stopped when the lid was closed.

This experiment disproves the explanation given for crab’s chirping. If the crabs are really making noise by rubbing their body parts against the shell, then a freshly molted crab will not chirp. The Slater appeared very soft and pink after molting. Its exoskeleton was soft with some secretions of the body. If it rubs the body to the shell in this condition, then the sound will be different to that of ‘chirp’ as the body surface is very soft.

If it is not the rubbing of skin at the shell which makes the noise, then what could be the reason for the chirping? It is not known by anyone what could be the exact reason. Probably, some hard chitinous plates inside their bodies might be responsible for that sound. The exoskeleton was affected by the molting, but the external surface around the pericardial area and the grinding plates will not participate in molting. This might be the reason for the crab to make chirping noise.