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Hermit crab shell exchange

By Slickrock Adventures on April 26, 2017

hermit crab belize

When guests first arrive on our island in Belize, we take them on a tour. In about 45 minutes we show them everything they need to know about the island for the week: where their cabana is, where the bathrooms are, how to check out and return our sport gear, where to find the cold beer, etc. It’s my job to conduct the tour, and one of the odd things that happens every single week is I can’t keep the tour moving because of hermit crabs. People see a hermit crab for the first time, and they come to a screeching halt. By Day 3 they are over it, but at the beginning, they are transfixed.

As the week goes on, people start coming to us asking why all the hermit crabs are collected together, in what looks like an impromptu convention, on the path near their cabana. And the answer is surprising: it’s a potential hermit crab shell exchange.

Hermit crabs do not have the ability to make their own shells. They have to move into someone else’s’ shell. Or someone else’s anything. I have seen them in film cans, shampoo bottle caps, and champagne corks! So when they are babies, they can’t move into a huge shell. The shell has to fit them. What this means is as they grow, they get too big for their britches, as they say. They get too tight, and they have to find a new shell and move out of their current shell and into the bigger one.

It follows that when that hermit crab abandons their shell, another, smaller, crab will want that one, and they will move out of THEIR shell, creating a new home for someone else. There it goes down the line, each shell that is abandoned gets smaller and smaller.

hermit crab shell exchange

Once you know about this, you will start to notice that there are not any empty shells lying around anywhere. If you happen to find one, put it on the path near where you walk by all of the time. In less than a half a day you will see not just one, but many crabs grouped around it. For even if that shell doesn’t fit one particular crab, he knows that this empty shell will create another available shell his size eventually. Hermit crabs are ALWAYS looking for a new, slightly larger, shell.

So what this boils down to is this: the premium piece of real estate is the largest shell. One Grand Daddy shell will provide homes for everyone. So in an odd reversal of the usual order of things, it is the largest creature that is at the biggest disadvantage. All of the other crabs will gang up on the big one, and pull him out of his shell! I kid you not! He dies, for he has nowhere else to go. Then everybody else moves up.

Sometimes one of these conventions doesn’t turn into an actual exchange. If there is no empty shell, they are actually trying to decide if they are going to gang up and pull the big guy out of his shell or not. All of the crabs feel each other for a while, and then they are just as likely to wander away as to take action. In this video, you will see that Larry Staples did find an empty hermit crab shell to place by his cabana, and it is causing quite a stir.

A shell exchange takes hours and hours. Jim from the dive shop used to tell a story of one trip where the whole group pulled up chairs and watched the entire exchange, and it took about 8 hours. He had to take them snacks and drinks, they wouldn’t leave! When he would stop by they would report on the latest: “Jim! The brown striped one just moved to a white shell!”