Aggregative behavior and intraspecific communication mediated by substrate-borne vibrations in terrestrial arthropods: An exploratory study in two species of woodlice

Gregarious behavior and aggregative phenomena among conspecifics in woodlice are thought to be a form of evolutionary adaptation to the terrestrial environment which has given these animals multiple advantages, e.g., against desiccation and predation. The reasons behind these phenomena, however, have not fully been clarified yet. This exploratory study has the aim to assess displacement and aggregation state relatively to the presence of substrate-borne vibrations in two different species of terrestrial isopods. To this goal, a circular arena was used to collect data from adult individuals of Armadillo officinalis, a stridulating species, and Armadillidium vulgare, a non-stridulating species, both exposed and non-exposed to micro-vibrations. Our results showed that exposed individuals of A. officinalis significantly react to micro-vibrations positioning themselves preferentially far from the vibrational source compared to non-exposed individuals of the same species. Furthermore, both the number of aggregates and of isolated subjects significantly increase in the presence of substrate-borne vibrations than in the absence of micro-vibrations. No statistically significant association with substrate-borne vibrations was found for A. vulgare for both placement and number of aggregates and of isolated subjects. Unlike A. vulgare, A. officinalis appears very sensitive to micro-vibrations which seem to represent a source of disturbance or potential danger. Substrate-borne vibrations seem to affect the capability of this species to aggregate leading to a greater number of aggregates and isolated subjects as if animals were a bit disoriented. This behavior might be related to a possible capability of this species to use micro-vibrations for inter- and intraspecific communication.