Many house plants are poisonous to pets, but some of them are safe for crabs.
Spider plants --(Chlorophytum comosum, also known as Airplane plants) are safe. Crabs will eat the long fresh leaves and the small white blossoms.
Aloe Vera --is on the safe food list, but many crab-keepers avoid it. My crabs have never eaten them.
Hen & Chicks --is on the safe food list, but my crabs didn't eat it very well.
Bromiliads --Most bromiliads are safe. Pineapple is one example of bromiliad that crabs are known to favor.
Fuchsia --(see comment by Pearl.)
(This entry will be edited as more info is discovered, but I wanted to post it now so that our readers can share their experiments and results with common house plants by commenting here.)
Here is a nice website that lists the general toxicity of common houseplants: