Among crustaceans, numerous aquatic species are obligate groundwater-dwellers, i.e., stygobionts; their most common adaptations are the absence of eyes and a general depigmentation. Among the most widespread Eurasian stygobionts are the amphipods of the genus Niphargus. They are reported not only from groundwaters but also from groundwater-fed springs, where the abundance of food is higher, but where they also experience the constraint of UV radiation during the day. The aim of this study was to assess if in spring habitats Niphargus amphipods show diel activity, in particular if they are able to exploit the resources during the night.