The list of critters that can safely exist with hermit crabs is fairly short.
Yes

- Isopods – Some species are beneficial tank cleaners – some are not safe tank mates for hermit crabs. We are working on a list for you!
- Springtails – beneficial tank cleaners
- Food/soil mites – harmless
In 2009 I introduced isopods to my crabitats.
Not Safe for Co-habitation
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- Fiddler Crabs/Halloween Crabs – aggressive diggers and are likely to eat molting hermit crabs.
- Earth worms, beetles, centipedes, crickets, praying mantis, roaches: May stress each other, over populate, disrupt/harm/ kill/ eat molters. Crabs may harm /kill them. May carry/spread disease/parasites, especially with over population.
- Centipedes – venomous
Millipedes – poisonous
Snails – Hermit crabs can kill snails
Frogs/Lizards – could harm each other, different habitat needs
Fish – inappropriate water for a fish