Ermine

• Bats count on their secret weapon, echolocation, to find and catch their flying prey, and in response, nocturnal insects have evolved interesting defences.
• Many silk moths, for instance, rely on a kind of sound-absorbing stealth cloak that makes them “disappear” from bat sonar.
• However, scientists have long been puzzled about the many earless moths that cannot detect their predators and are too small for decoys.
• We recently discovered that even earless moths, such as ermine moths (Yponomeuta), use acoustic signals as a defence against bat attacks.

Protective wing beats

When we studied the ermine moth’s wing under a microscope, it became clear that one part of the wing stands out from the rest. While most of it is covered by small hairs and scales, one patch of wing is clear and located adjacent to a corrugated structure of ridges and valleys. In our new study, we found this structure produces sound perfectly tuned to confuse bats.

• As the drum skin is struck by a drumstick, the skin vibrates at its natural frequencies and transmits these vibrations into the surrounding air as sound.
• In ermine moths, the clear patch in the hind wing serves as the drum skin, while the corrugated structure of valleys and ridges act as drumsticks.
• During flight, the moth’s wing makes the ridges snap one after the other in a sequence.
• To our team of biologists and engineers, these wing structures are fascinating because they rely on a mechanism that we teach our engineering students to avoid.

Inspired by nature

• One example is engineers designing morphing structures for future aircraft wings that autonomously adapt their shape to perform better when the environment changes.
• The aeroelastic tymbal of ermine moths embodies this concept and demonstrates how nature can be an inspiration for new technology.

• BB/N009991/1) and the Engineering and Physical Sciences Research Council (grant no.
• Alberto Pirrera has received funding for this research from the Engineering and Physical Sciences Research Council (grant no.
• 530777/472285) and the Engineering and Physical Sciences Research Council through the EPSRC Centre for Doctoral Training in Advanced Composites for Innovation and Science (grant no.