The acoustic properties of clear patches on moth wings and their roles in acoustic camouflage

Abstract

Bats and moths are in a coevolutionary predator and prey relationship, both trying to better their acoustic abilities and properties to increase their survival. Moths are known to have adapted for visual camouflage in both their looks and behaviour. This has been helped in a high number of moth species by their clear patches, which are areas of transparency that break up the outline of a moth. The structure of the clear patch also varies, with some species like Attacus atlas having scales on the clear patch, whilst species like Copaxa witti are barren of structures. The acoustic properties of the clear patch have not been recorded, which is what this study set out to do. Acoustic tomography and sound transmission measurements were used, like other studies, to look at the directionality of reflections, as well as the percentage of reflection, transmission, and absorption for both the clear patches and scaled patches. These experiments used both biopsy punches from the moth wings, as well as small rectangular segments. Both contained either just the scaled section of wing, or both scaled section and clear patch. The results showed that in general, the clear patch had a lower directionality than the scaled patches, acting more specular in their sound reflections. The scaled patches also had significantly higher absorption than the clear patches, with different species using transmission or reflection to create disruptive colouration, which varied depending on the structure on the clear patch. The species with ‘haired’ clear patches were found to have significantly different results from those with non-scaled clear patches, showing that the hairs also have absorptive properties. The conclusion of this study is that clear patches act differently to scaled areas in terms of their acoustic properties. The barren areas of wing membrane act mirror-like with how they reflect sound, implying that moths have evolved clear patches that contribute to both visual and acoustic camouflage.

Date of Award	21 Mar 2023
Original language	English
Awarding Institution	University of Bristol
Supervisor	Marc W Holderied (Supervisor)