This study was conducted to determine whether mayfly nymphs (Stenonemasp.) have the ability to detect and respond to potential chemical cues from crayfish (Orconectes rusticus) by adopting anti-predator behaviours, and to investigate whether any potential responses would differ under exposure to different light conditions. The average number of mayfly nymphs displaying ‘scorpion' posture, and the average duration of this behaviour were significantly greater during exposure to crayfish conditioned water than during exposure to unconditioned water. The results also suggested that there was a decrease in drift behaviour and horizontal movement in conditioned water trials relative to controls, as well as an increase in refuge use. However, with the exception of refuge use, differing light intensities did not have a significant effect on the observed prey reactions, although responses did appear to be slightly stronger during exposure to lower light levels relative to higher light conditions. This research provides new insight into the role of invertebrate predators and chemical cues and their influence on the behaviour of an important benthic prey species.