InvertInsects: The energetic cost of inverted locomotion in insects.

Walking on inverted surfaces— or upside down— is crucial for insects when foraging, evading predators, or safely laying eggs underneath leaves. Animals often choose how to locomote depending on the associated energetic costs; yet, the costs of locomotion on inverted surfaces remain unknown, and existing theories of locomotor energetics yield contrasting predictions when extrapolated to inverted locomotion. This gap limits our understanding not only of insect biology but also of what determines animals’ energy expenditure when they locomote. To address these issues, I will quantify the metabolic and mechanical costs of inverted locomotion in stick insects of the species Sungaya aeta, chosen as a model for their climbing ability, ease of husbandry, and wide size range. Methodological barriers have so far hindered such studies: no system allowed insects to walk freely and continuously on inverted surfaces while compensating for their motion, thus allowing respirometry measurements. Moreover, marker-based tracking interfered with their movement, and markerless tracking required laborious manual annotation. To overcome these barriers, I will integrate a respirometry and a markerless motion capture system with a world-unique infinite walking plane, developed by the host lab, enabling untethered and self-guided locomotion at any incline. With this setup, I will quantify (i) the energetic costs of locomotion across surface inclinations spanning 360°, (ii) how these costs change with the payload carried by the insect, and (iii) how they scale with body size. InvertInsects will shed light on the physiological demands of a widespread, ecologically relevant, yet understudied insect behaviour, and simultaneously advance our theories on the energy demands of animal locomotion. In the long term, its outcomes may inspire biomimetic robots with improved climbing efficiency and support sustainable agriculture and biodiversity conservation by controlling invasive insects’ mobility.