Effects of Sex and Substrate Type on the Inversion Risk and Righting Behavior of Flamboyant Flower Beetles (Eudicella gralli): Implications for Habitat Design and Beetle Welfare

Despite their prevalence in zoological collections, the welfare of zoo-housed insects remains underexplored. This study investigates the influence of substrate type and sex on the inversion risk and righting behavior of flamboyant flower beetles (Eudicella gralli) at Cleveland Metroparks Zoo. We utilized remote cameras to record the behavior of beetles (n = 8 females and 8 males) across four substrate conditions (mulch, leaf litter, wood chips, and twigs) over a 20-day period. Behavioral data were collected via a combination of interval scan sampling, continuous all-occurrence recording, and keeper logs. Statistical analyses revealed that the interaction of sex and substrate type significantly impacted time spent inverted (p < 0.001) as well as the duration of inversion events (p = 0.01). Most notably, males on the mulch substrate spent the greatest amount of time inverted (i.e., 46.7% of observations), had the longest inversion durations, and most frequently required keeper-assisted righting. Locomotion was the primary cause of inversion events across all conditions, with conspecific interactions contributing minimally to inversion events. Righting methods varied by substrate, with self-righting and substrate-assisted behaviors more prevalent on wood chips and leaf litter substrates, while conspecific assistance was more common on mulch. These findings underscore the importance of substrate selection in mitigating welfare risks associated with inversion in scarab beetles. We recommend a heterogeneous substrate composition incorporating soil/mulch, leaf litter, and elevated substrates to enhance righting opportunities, reduce the need for keeper intervention, and promote naturalistic behaviors. This study contributes to the growing body of literature on invertebrate welfare and provides actionable insights for evidence-based habitat design in zoological settings.