What does the crab say?

Many different animals use sound as a way to communicate with one another. They bark, howl, yip, chirp, sing, growl, in order to talk with other members of their species. They use sounds like this to let others know where they are, to attract mates, for recognition, and even for hunting!

You might not think about it, but crabs use sound to communicate with one another too.

crab gif

Although it’s not quite like this. Source: http://giphy.com/gifs/cheezburger

There are two main groups of crabs that use sound as a means to recognize one another or attract mates. This is what inspired my independent project; I looked at how our local green shore crab, Hemigrapsus oregonensis, responds to sound. Something I didn’t know before I started this project is that these little guys actually produce sounds to communicate too.

The use of sound as communication in crabs has been well documented in fiddler and ghost crabs. The males of these groups will produce sound during the mating season, to attract females to their burrows. “HEY! I’m over here! Let’s get … together” C’mon guys, let’s keep it PG.

Fiddler crabs will have an enlarged claw that they use in combat and courtship. But aside from that, they actually strike their large claw off of the ground to produce sound. It is thought that this serves as a way for males to alert females of their presence during the mating season.

fiddler crab cartoon

They don’t actually fiddle, like their name suggests  Credit: Steve Timko

Ghost crabs use sound in a similar way, to alert females to their presence, for the purpose of mating. However, the way these guys produce sound is actually quite different. They do it in much the same way that a cricket does, through a process called stridulation. Crickets have structures on their legs that produce sound when they rub them together, and ghost crabs do too. Well, not on their legs, but on their claws, which is pretty cool!

FloridaGhostCrab

This is a ghost crab. It’s the cutest. Credit: Tim Quade

What I find super interesting is that the green shore crab actually uses stridulation too! The structures necessary for this are only found on males in this species. They produce sound during the mating season, like the other crabs, but for a different purpose. When males want to mate with a female, they will grab on to her. Sometimes there’s a mistaken identity issue, and males will grab on to other males. When this happens the little guy that was caught will rub his claws together to produce sounds that let the other male know that they are indeed, male. I mean, unless they swing that way, in which case whatever floats their boats.

IMG_4451

Here’s a little male green shore crab,  he was quite the escape artist during my experiment.

Crab behaviour is pretty cool, and researching this unique phenomenon in crabs was an awesome topic for an independent project. There’s still a lot of work to be done in assessing how acoustic communication works in crabs, but that’s half of the fun!

If anyone is interested in learning more I suggest reading some papers by Dr. Kenneth Horch, he’s done some really cool work on how ghost crabs detect sound.

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