Lovely addition to the tank but they do hide.
Lovely small freshwater crabs that whilst are very small, and tend to be largely anonymous unless hungry enough to forage. I received crabs which were all around the 1 CM diameter shell span, but their legs stretch out and are oversized in proportion.
They are shy and hide in the roots, or in small cracks in drift/plants but do venture out when the lights are off, or if they particularly hungry. Colouration seems to vary and mine were both white and beige/brown. As long as you expect them to be shy and not hugely active you'll be happy.
The other approach is to house them in a smaller 15 or 20L tank - you may then see them more often. I have a Fluval Spec V 19L and am strongly considering buying more to add to this planted tank which is home to yellow Neo shrimps.
Overall I would happily recommend these wee crabs, they seem hardy and very easy to accommodate as long as you have places for them to hide. A matured tank would be better as they filter feed a lot of the time and a newly setup tank may not have the bio benefits required for them to feed. They would be very easy targets for fish and would be expensive snacks, so bear that in mind. I keep them in a dedicated shrimp tank and they seem very happy.
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