Introduced in Italy in the 1980s for aquaculture enterprises, the red swamp crayfish, Procambarus clarkii, has invaded many water bodies, giving rise to breeding populations that now threaten freshwater ecosystems. An understanding of the spatial behaviour of this crayfish could be the baseline for future research aimed at control and management. Following the same pattern as other freshwater decapods, P. clarkii, studied in an irrigation ditch system in Florence, Tuscany, displayed stationary phases (several marked individuals were recaptured in the area) interposed with nomadic bursts of movement (many marked crayfish disappeared). With a few exceptions, nocturnal activity prevailed in almost all the seasons in two different analysed habitats (irrigation ditches and the Massaciuccoli Lake, Lucca). However, in the laboratory, locomotion occurred mostly at daytime. Although still prevailing, P. clarkii's nocturnal activity appeared puzzling, because some of its major predators are nocturnal and this species is mostly herbivorous. The intercalation between stationary and wandering phases leaves open further promising studies on social structures in the field.

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