Artificial light at night (ALAN) has emerged as a significant ecological disruptor, affecting various behavioral and physiological processes in numerous species. This study investigated the impact of ALAN on the risk-related behaviors and activity patterns of the ground-dwelling isopod Porcellionides pruinosus. Isopods were exposed to one of three different illuminance conditions (<0.01, 1 and 10 lx) over a period of 14 consecutive nights. Behavioral assays included emergence, open-field, habituation to a looming stimulus, and spatial navigation tests. Additionally, the distribution and activity patterns of the isopods within the terraria were monitored. Our results indicate that ALAN significantly disrupted the repeatability of risk-related behaviors, suggesting individual-level behavioral alterations. At the group level, ALAN-exposed isopods exhibited prolonged freezing durations in response to a looming stimulus, increased shelter-seeking behavior and reduced dispersal in the terrarium. These findings suggest that ALAN-induced transformation of activity pattern of isopods is linked to the adoption of more prudent behaviors. A similar phenomenon may affect the activity pattern of other ground-dwelling invertebrates, leading to severe alterations of the soil invertebrate community.
