The crayfish Orconectes rusticus can form a learned association between alarm odour (an unlearned signal of elevated predation risk) and a formerly neutral odour. In this study the odours of gyrinid beetles and of the snail Campeloma decisum were each paired with alarm odour and subsequently those odours significantly reduced feeding behaviours in the presence of food odour. To test for second-order (=conditioned) reinforcement, crayfish were first exposed simultaneously to one of the neutral odours and alarm odour and later exposed simultaneously to the two formerly neutral odours. When tested with the second neutral odour (which was not paired with alarm odour) the crayfish showed significant reductions in food-related behaviours, thus demonstrating second-order conditioning.