Plastic Behavioral Responses to Ambient Relative Humidity Influence Aggregation in a Large Gregarious Insect

Kryger A.; Huang K.; Tabrizifard K.; Yang J.; Martin A.M.; Swierk L. · Ethology (2026) · DOI: 10.1111/eth.70026

Resumen

Aggregation behavior in arthropods is often a response to environmental stressors, particularly desiccation risk. While this is well documented in small-bodied and larval arthropods, less is known about whether aggregation behavior provides similar benefits to adult and/or large-bodied insects. Here, we investigate whether aggregation behavior in adult Madagascar hissing cockroaches (Gromphadorhina portentosa), a large insect species, is modulated by ambient relative humidity (RH). We exposed mixed-sex groups of adult cockroaches to alternating high (75%–90%; “wet-season”) and low (50%–65%; “dry-season”) RH in a controlled laboratory setting and measured aggregation behavior over multiple weeks. Aggregation was significantly more likely to be observed under low RH, with a greater proportion of individuals aggregating. RH did not affect the sex ratio of aggregations. These results support the hypothesis that aggregation behavior in adult G. portentosa is, at least in part, a plastic and adaptive response to arid conditions, likely enhancing water retention by creating a humid microenvironment. Our findings highlight the importance of behavioral plasticity in large-bodied insects facing fluctuating environmental conditions and suggest that increasing aridity due to climate change has the potential to impact the ecologies of G. portentosa and other similarly large, forest-floor arthropods.