I would have told you just the opposite, to my knowledge they need quite a bit of humidity. My good friend got 10 hermit crabs 3 years ago and had only lost 1 of them... that's a pretty good record if you ask me. She keeps them in a big tank with a fair amount of humidity. I know she has a humidity gage, but I don't know what she maintains it at. They are from a tropical setting, so it would make sense that they need humidity.

I would suggest googling it and see what several different sites say.