They eat anything and everything. Don't worry about her bothering your fish...very peacful. Do make sure there are no openings at the top of your tank or she will get out. Mine was hanging out on top of my acrylic tank and under the canopy within 4 hours of arrival. I plugged the holes with filter floss. Also, make sure it can get to the surface and perch for air or have a bubble bar on the bottom. As far as food, pick up some Hakari crab cuisine or comparable (hermit crab meal, etc.). This type of food is needed because of the high calcium content for the shell. Mine was shy for about a month until he figured out he was completely safe. Now he is everywhere. He's actually a pain when I'm trying to clean and fix plants. Always in the way looking for a handout. Also, don't be alarmed to find an upside down crab somewhere legs up...they molt and shed thier entire shell every few months when growing. I found this and thought "oh no", and then I saw the crab hanging out on a powerhead. He was a lighter color and stayed up there for protection for a few days while his shell hardened and resumed its natural brown/red color. Enjoy.