Reason:

1, due to the serious pollution of the river water now, it is not clear whether the river small crabs survive in a clean environment, if the river water is not clean, the crabs drink this water, the crab body will remain toxic substances, you can not eat.

2, the river small crabs can clearly know from which river, if the river water can usually be used to wash vegetables, you can eat, but do not eat if you are not sure, sure and then eat.