Pilli_pala,
If you'll look at the substrate blacklist (
http://www.hermitcrabparadise.com/crabc ... eslist.php), you'll see that wood shavings/sawdust is not good for crabs. Depending on what kind of wood it's from (cedar or pine especially), it will actually kill your crabs due to its insecticidal qualities. Additionally, gravel is also on that blacklist - it won't allow your crabs to dig into it and make their cave for molting. I recommend that you get rid of both of those in your tank and either get all sand (not anything labeled "CalciSand" or "Hermit Crab Sand" or anything that mentions being a calcium source) or coconut fiber (Eco Earth being the most common brand).
Your tank is a bit small for four crabs as well. Crabs in the wild will run around over two miles in one night, so you need to get them a bigger tank as soon as you can. Ten gallons would be much better than what they have.
Do you offer any sort of salt water? If not, please look at
http://www.hermitcrabparadise.com/crabc ... /water.php to see why they need salt water and what brands are okay for you to use for them. Bottom line up front, they can die from no salt water, although it will take a while.
Do you dechlorinate water before giving it to them? If not, the chlorine will blister their gills and will eventually cause them to suffocate and die. Otherwise, you could offer them distilled water with no minerals added.
What is a suitana?
Also, that "straw" isn't any sort of pine material, is it? If it is, it will cause your crabs to die. If not, then it should be fine.
Do you have a gauge to measure temperature and humidity in the tank? You need to keep the tank between 70-78 degrees F at all times, and the humidity needs to be between 70 and 80%. Otherwise, they won't be able to breathe - they have gills to breathe the humidity.
Also, please don't put their tank in direct sunlight; it can over heat them.
Sorry if I sound mean - I am running late but wanted to get this information out there for you.
