Abstract

Body size plays an important role in predator-prey interactions, but its evolution is often limited due to all sorts of constraints. The arms race between bats and moths provides great opportunities to study body size evolution and associated traits across a wide range of species. Nocturnally-active moths are in particular limited in evolving larger bodies, as any increase in echo-acoustic reflective surface will put them more at risk of a bat's sonar system. Here we assessed whether moths can escape bat detection in a size-dependent way by increasing their acoustic camouflage through ultrasonic absorptive body scales. We used an automated setup to 3D scan a total of 110 moth specimen, from eight different families of Lepidoptera using a biomimetic bat head. We carried out three different ensonification experiments with intact, partially shaved and fully shaved moth specimen to relate the level of acoustic camouflage to various body size measurements. Comparing shaved versus intact specimen we found a clear reduction in target strength, although the effect strongly depends on frequency range as well as body size. The stealth coating provided by sound absorptive body scales can reduce prey detectability up to 365 cubic metres and is in particular beneficial to larger species. The level of acoustic camouflage did not covary with other anti-predator traits, such as ultrasonic ears and appears to be an all-round anti-predator strategy. Acoustic camouflage through stealth coating thus allows moths to escape from the allometric relationship between size and detection risk, thereby enabling species to evolve larger bodies.