We studied the rate of oxygen consumption and morphometric parameters in intertidal snails Littorina saxatilis and L. littorea (Littorinidae, Gastropoda). Adult snails with body weight more than 0.1 g exhibited higher rate of oxygen consumption in the air environment in comparison to the aquatic one, whereas no difference between these types of metabolism were found in small snails. Animal activity explains the difference between aerial and aquatic respiration only partly. We propose that higher level of aerial respiration causes migration of large snails to sublittoral zone, which is more fitting for such animals. We discuss possible ecological and evolutionary mechanisms associated with different values of standard metabolism under different conditions