The role of olfactory cues in settling behavior of the isopod Armadillidium vulgare (Isopoda: Armadillidiidae)

The aggregation behavior of isopods like Armadillidium vulgare functions to limit desiccation and reduce metabolic rates. Aggregation may also function as a cooperative form of communication enabling A . vulgare to relay habitat quality to conspecifics. Grouping is stimulated by social interactions and physical cues and aggregation pheromones in feces. This study examines whether chemical cues, in the absence of social or physical cues, will influence settling behavior in A. vulgare. We determined whether a lone conspecific would spend more time on the side of an arena with no previous isopod cues versus the side that previously held conspecifics but was absent any discriminating physical cues, such as disturbed earth or exuviae. We also determined whether the number of previous occupants influenced settling behavior.A Chi-Square Binomial test, and an ANOVA followed by a Tukey’s Post Hoc Test were used for data analyses. Isopods spent more time on the side where five or ten previous conspecifics had been housed but not a single conspecific. Lone isopod movements across a median line decreased in arenas that previously held occupants. Thus, olfactory cues from conspecifics can stimulate settling behavior, and lone conspecifics prefer an area recently abandoned by a grouping of conspecifics versus a previously unoccupied area. Settling behavior appears to be stimulated by chemo-sensitive stimuli from conspecifics in A. vulgare even in the absence of conspecifics or physical cues.