Stress can alter adaptive behaviours, and as well either enhance or diminish learning, memory formation and/or memory recall. We show here that two different stressors have the ability to alter such behaviours in our model system, Lymnaea stagnalis. One, a naturally occurring stressor - the scent of a predator (crayfish) - and the other an artificially controlled one - 25 mmol l(-1) KCl - significantly alter adaptive behaviours. Both the KCl stressor and predator detection enhance long-term memory (LTM) formation; additionally predator detection alters vigilance behaviours. The predator-induced changes in behaviour are also accompanied by specific and significant alterations in the electrophysiological properties of RPeD1 - a key neuron in mediating both vigilance behaviours and memory formation. Naive lab-bred snails exposed to crayfish effluent (CE; i.e. the scent of the predator) prior to recording from RPeD1 demonstrated both a significantly reduced spontaneous firing rate and fewer bouts of bursting activity compared with non-exposed snails. Importantly, in the CE experiments we used laboratory-reared snails that have not been exposed to a naturally occurring predator for over 250 generations. These data open a new avenue of research, which may allow a direct investigation from the behavioral to the neuronal level as to how relevant stressful stimuli alter adaptive behaviours, including memory formation and recall.