The information at present available suggests that, when adult,Nucella lapillusmay prey upon a considerable number of different species, but that the diet of recently hatched dog‐whelks is rather more restricted. The food preferences of youngNucellahave been investigated and it has been concluded that, while the diet of young and adult animals may differ to some extent, it is probably equally varied at all ages, and that cannibalism may be a frequent occurrence amongst all age groups.It has been determined that the size of the prey influences the selective predation ofMytilusbyNucella.Dog‐whelks show a marked preference for mussels in the 1 to 3 cm size range which may possibly be identified chemotactica