Hermit Crabs are quite complicated when it comes to behavior. Every single hermit crab is different and you will never meet two that are the same. Some are aggressive, some are submissive, some are outgoing, and some are truly 'hermits' that prefer to just be left alone. Some like to eat fish, some will only eat fruit. Some seem to be active and exploring 24/7, others barely ever come out of their shell. But there are a few basic behaviors that you can expect from every single hermit crab.
Pinching: Yes, quite honestly, hermit crabs pinch. If properly handled there are hermit crabs that will never pinch. Then again, there are hermit crabs that just seem to love hearing you wince when that little claw grips onto your skin. Yes, it hurts. But you have to realize this is absolutely natural behavior. In the wild hermit crabs will pinch when they feel threatened or if they think they are going to fall. Make sure to handle hermit crabs safely, over a soft surface, and never with more than a foot falling distance. Be patient and prepared. Hermit crabs aren't out to attack you, but under some circumstances they may feel the need to grip onto your palm.
Nocturnal Activity: Hermit crabs are night dwellers, they absolutely love the stars and the moon. And they get their most active in the dark hours. Be prepared for little hustling of tiny feet in the late hours of the night. If you are a light sleeper, your bedroom probably isn't the right place for your crabitat. On the other hand, if you yourself tend to stay awake into the late hours you'll find much company in these little fellas who will happily join you in your nighttime activities.
Molting: Hermit crabs molt every 10 to 18 months. This is the process of a hermit crab discarding its 'exo-skeleton' or outside layer of skin so that it can grow larger and rebuild it's next exo-skeleton. This process usually takes around 4 weeks and happens in a secluded underground tunnel.
Little Quarrels: For the most part hermit crabs are very friendly creatures, and are social by nature. But from time to time a little quarrel will occur. Most of the time no human intervention is needed. Hermit crabs squabble over all sorts of things and quickly forgive and forget. Most of the time the only disagreement noise will be small little chirps and the argument will be finished within a matter of minutes or sometimes even seconds.
Eating: Hermit crabs are scavengers by nature. They eat everything from seaweed to dead fish to fallen fruits and wild grass. They love food and need a diverse diet of many different things.
'Bathing': Hermit crabs don't necessarily 'bathe', but they do visit saltwater and freshwater ponds habitually to take a dip. Some would say they're swimming, some say 'wetting their gills', and some say they're bathing. All of the above may be true, but the fact of the matter is that these little creatures love water and should always have access to a good amount of it.