Chirping! The mysteries of hermit crab vocalization
My crab makes noise! It isn't enough that hermit crabs are cute and fun pets, but they also make the neatest sound. It has been described as sounding like a combination of any of the following: a creaky bed, a rusty door hinge, a croaking frog and a chirping bird. It is hard to explain the exact sound, so I have an audio file here of the Ecuadorian crabs Pablo Ting and Jesus having a rather heated discussion.
How do they do that? Scientists call the noise our pets make "stridulation." They believe the noise is caused by a crab rubbing its body parts together or rubbing against the inside of their shells. True, when you hold a 'stridulating' crab, you can sometimes feel vibrations from their bodies.
Are we sure that's how they make the noise? Nope. As the cat's purr is a mystery, so is the hermit crab chirp. Here follows an amazing story of why I don't believe the scientific explanation of their chirping:
One day I checked up on one of my crabs in isolation -- Slater, a large Ecuadorian who was in 'molting posture' the night before. I raised the lid of the isolation tank and Slater started chirping angrily at me -- he was in mid-molt! I shut the lid, but then realized that there were other crabs in the tank that could have been making the noise. I opened the lid again and the chirping started up again. I removed the other three pre-molt crabs (who hadn't started digging yet) and bent close and listened: Yep, it was Slater.The question this presents is obvious: If indeed the chirping noise were made by a crab rubbing its legs/claws against the each other or its seashell, how could a freshly molted crab stridulate?? Slater was soft, pink and very pliable (I could tell because he was wiggling his claws around sideways, something he could NEVER do once the claws are hardened). His exoskeleton was soft with body secretions. If at this point he rubbed his soft pink body against itself or his seashell, the resulting sound would be more like a 'squish' than an irritated, insistent chirp!
So then how can they make that noise? Nobody knows for sure. It is my personal belief that there are some kind of hard, chitinous plates inside their bodies somewhere that make that noise, and that it is not made externally. When a crab molts, as far as we know, only the OUTSIDE exoskeleton is affected. The tough casings surrounding the crab's pericardial area and its grinding plates (similar to a gizzard in a bird) are not affected by the molt. That is how I believe Slater made his noise at me, from within his body.
So there it is, in a crab-shell, a brief discussion of the crab chirp. Of course I couldn't post this page without Pablette adding her final words on the subject. Click here to hear her explanation of why hermit crabs chirp.
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ęChrista Wilkin 2008