Biology/Natural History: Often found in as a group of several. Graze on diatoms from rocks and algae at low tide. On mechanical stimulation, the marginal tubercles or papillae produce secretions that repel potential predators such as seastars, especially Leptasterias hexactis, which retreats from an encounter. Hemigrapsus nudus will eat dead individuals but not live ones. Lays a gelatinous mass of 6-40 encapsulated eggs. Hatch as young juveniles.