This arthropod is a relative of the familiar garden sow bug or isopod. The rock louse, a scavenger, is often seen in great numbers on the rocks or cliffs during certain times of the year. The rock louse is certainly in transition because it will drown if it is placed directly in sea water. It is also the only index organism of the splash zone that does not rely on the sea to reproduce. The young animals hatch directly from the eggs that are carried by the female. Other organisms of the splash zone must shed their eggs into the tidal water and then reinvade the splash zone from the sea.