I was inspired to look up some info on hermit crabs after seeing the above image, and came to find out that despite their name, they are actually quite social creatures. The fact that they often fight over quality shells didn't come as a surprise, but they apparently also exhibit cooperative shell-acquiring behaviors, which I thought was terribly interesting. Here's a video of it:
Apparently when a hermit crab comes across an empty shell too big for it to use, it may wait nearby instead of moving on. Eventually a large number of crabs may gather around it, and the smaller ones will start to climb onto the backs of the larger ones. Then, when one of the crabs decides to make use of the empty shell, the next biggest will use the now empty shell of the first, the third smallest will climb into his, and so on down the line. It's been dubbed a "vacancy chain." I imagine some fighting would still occur if more than one crab of the same size joined the chain, but the generally cooperative nature of the behavior adds another layer of charm to these odd little critters for me.