hermit crabs...

Yes, with mixed results. Some hermit crabs will literally kick out a current resident (crab or snail) in order to go house shopping, so make sure you provide lots of empty shells in a variety of sizes. A dedicated Otherwise, mixing is fine.
 
I have blue leg, red leg, dwarf red leg, scarlet, and a couple of white crabs (cant remeber the name). In the snail category, I have turbos, nassarius, bumble bee, and two other varities that I can not remeber (hitchhikers). The bigger red legs scarlets like to check out the smaller turbo snails for housing, but everything pretty much gets along as far as I can see.
 
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