Hermit Crab Molting/ Fighting??

Question
I bought two small crabs the same size for my son for the first time and noticed one start digging all the time. After about a week he fully went underground, I was worried but could hear him under there. I did the smoothing sand technique to catch him coming out but he didnt, and after 5 or so days, I walked in and he was out!
But he hadnt molted or nothing. He went for a feed tho...I watched them for hours after he came out and I noticed he started following and picking on the other one, while the other one just wanted to get away.
Anyway, wanting to know what's going on....does he want to molt and cant? Or is he stressed? Why pick on the other one?
Also, when they molt and go under, do they emerge molted? And do they leave the other shell under? Or do they come out as they went in, then chose a shell aboveground????
Dont understand!!!!

Answer
Okay, let me try to break down your questions.


does he want to molt and cant? Or is he stressed?

Sometimes crabs dig just to dig. They have good fun tunneling around. Stress can be a factor but if he was active down there and not just hiding, he is most likely doing because he wants to.

Why pick on the other one?

It depends on his behavior. As long as it doesn't move beyond chasing, waving antennae, and shoving it's fine. If he grabs him or locks onto his shell you've got shell aggression and need to look into getting more properly chosen shells. You can try dipping both of them in the water pool too, that will sometimes calm them down.

Also, when they molt and go under, do they emerge molted?

Yes, they do it completely under the substrate


And do they leave the other shell under? Or do they come out as they went in, then chose a shell aboveground????

Molting and changing shells aren't the same. It's unusual for a crab to molt and do a shell change at the same time. They do not need to leave their shells to molt, and usually wont. Sometimes the will change shells in the days before they go under, sometimes they will come up and change shells. A crab that comes up naked will usually have lost his shell due to it getting stuck, or is in distress. About half the time these crabs re-shell quickly, half the time they are in distress and don't do as well.