Self-righting physiology of the ladybird beetle Coccinella septempunctata on surfaces with variable roughness

Insects such as cockroaches and locusts self-right swiftly to reduce chances of being attacked by predators. Compared to these insects, ladybirds have shorter legs hidden inside highly domed elytra so self-righting is of great challenge if using strategies of abdominal arching and/or leg swinging. Specifically, ladybirds live in over-ground environment with clusters of vegetation so they are prone to self-right from various natural substrates, such as soil, bark, and leaves. However, self-righting strategies under such complicated environment packed with multiple surfaces remain elusive. In this combined experimental and theoretical study, we examined and quantified self-righting physiology of ladybirds (Coccinella septempunctata) on surfaces with varying roughness. Most ladybirds self-right in 15.00 s with a success rate of ~100.00% within 3 attempts using either legged or winged strategies, and the self-righting strategy is strongly associated with the surface roughness. Righting on a coarser board (R_a = 124.62 μm) is performed by swinging the legs to attach and hook the protrusions on the rough surface. However, if self-righting occurs on a smooth surface (R_a = 6.69 μm), both the elytra and hind wings deploy to alter the body orientation to roll over. Considering the effect of surface roughness, we analyzed the self-righting mechanism by a mathematical model, and uncovered that contact status between the claw and surface microstructures affected the arm of force required to self-right, which leads to the binary strategic selection. Our quantification of self-righting on diverse surfaces not only deepens understanding of ladybird's self-righting but may inspire new means of evaluating its environmental adaptability.