Monk crabs are not poisonous. Wash the sediment before eating and start cooking. Creatures that eat sediment (such as razor clams), such as short-fingered monk crabs, need to be washed before eating. and the work of making it spit out silt. If the sediment is not washed out, the food will taste like sediment in your mouth and you will not be able to recognize the original taste of the food.