Bats rely on echolocation to find and capture their flying prey. Therefore, nocturnal insects have developed a whole host of defense mechanisms to circumvent this system. For example, many silk moths rely on a kind of cloak that absorbs sound and helps them “hide” from bats' sonar. Some large moth species have reflective attractants that direct bat attacks away from their bodies and toward the tips of their wings.
In addition, insect ears play an important role in their defense. This allows them to pick up echolocation sounds from bats and fly away. They can also use their sensory perception of location to bombard the attacking bat with ultrasonic sounds that disrupt sonar.
However, there are many butterflies that are too small to protect themselves with attractants or cannot detect danger because they do not have ears. How do they protect themselves from bat attack?
British researchers searched for this question and found an answer. They discovered that deaf moths, such as spotted moths, also use acoustic signals to defend against bat attacks. In their hind wings there is a small structure that emits a powerful ultrasonic signal that disrupts bats' sonar.
Moths are not aware of this defense system, and therefore cannot control it, because they do not have a hearing system. The sound production mechanism is linked to the flapping of their wings.
Flutter protected
When you look at a spotted butterfly's wings under a microscope, you'll find that one part of it clearly stands out from the rest. The striking part is smooth and hairless and is located next to a frilled structure, while most of the wings are covered with hairs and small scales. This wavy structure produces sound at the perfect frequency for disorienting bats.
Sound is created by pressure waves traveling through a medium, such as air, and vibrations are needed to produce these sound waves. A common example of how vibrations amplify sound is the action of a drum, where the head is tightly extended over the cavity. When this head is struck, it vibrates and amplifies sound waves in the air around it.
The wings of spotted moths use a similar mechanism. The bright spot on its rear wing acts as a drumhead, while the sinuous structure of the wing takes on the role of drumsticks. When moths fly, wing movements cause the edges to “break” in a row. This causes the bright spot to oscillate which amplifies the volume of the resulting sound, which is the warning signal.
Some species of eared moth can make similar warning sounds, but the spotted moth is the only moth we know of that uses the drumming principle.
Applications
The protective mechanism of earless mites could inspire new technologies. For example, the structure of a spotted butterfly's wing can be used to inspect infrastructure integrity. The pavilion structure can form the basis for structural acoustic monitoring, as the substructure emits sound when overloaded. This reduces the risk of damage and collapse.
In addition, engineers can apply wing structure to aircraft wings. The wing can then independently adapt to the environment in order to provide better performance.
He can also change robots. At the moment, robots are still mainly made of metal and plastic, but with the wavy structure it will be possible to make them from liquids and gels.
