Hermit crabs form gangs and steal from other crabs!

One of the most interesting things about hermit crabs is that they have to keep seeking new homes as they get larger. They have long, spiral-shaped abdomens which are incredibly soft, and as a result they need to use shells as a protection from predators. When one crab moves into a bigger shell, the other crabs often form a line from biggest to smallest, so that everyone gets to upgrade to a bigger shell!

If you think that act of survival is impressive and charitable, just wait until you read what crabs do to each other if they become jealous! Hermit crabs are known to gang up on another hermit crab if they perceive that crab to have a better shell. Hermit crabs will physically pry another hermit crabs home away from it, and then they will compete for that shell!

It ain't easy bein' a crab.

(Source)