How Butterflies Hear

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How butterflies hear, according to articles in Journal of Experimental Biology , vol. 212, p3533, and ScienceDaily 22 Oct 2009. Insects have been found to have ears on just about any part of their body. These usually consist of a taut membrane that vibrates when exposed to sound and is connected to nerve cells. Scientists at Bristol University have studied the ears of a tropical butterfly named Morpho peleide that has ears located at the base of the forewings. The membrane of the ear has a dome inset into it, making it distinctively different to other insect ears. To see what effect this unusual ear structure had on what the butterfly could hear, the researchers scanned the membrane with a tiny laser beam whilst the membrane was exposed to sounds of different frequencies. They found that lower pitch sounds cause vibrations only in a part of the outer membrane while higher pitch sounds caused the entire membrane to vibrate.

The researchers also made recordings of the nerve signals from different parts of the membrane. They concluded that the unusual structure of its ears enabled this butterfly to hear a wide range of sounds and is very sensitive to low pitched sounds. They suggested that sensitivity to lower pitch sounds enables the butterfly to hear the beating of birds' wings, while the ability to hear higher pitches enables it to hear birdsong. They wrote: “We suggest that this remarkable variation in structure is associated with function that provides a selective advantage, particularly in predator detection.”

ScienceDaily

Editorial Comment: “Selective advantage” is a typical evolutionists’ non-explanation for how something came into being. The ability to hear low pitched sounds may be a selective advantage in a place where birds eat butterflies, but it does not explain where this structure and its associated nerves came from. We hope some scientists will follow up this study with one on whether having this structure really does enable butterflies to avoid being eaten by birds. We predict they will find it makes little difference since studies of other butterfly functions supposed to provide protection from predators, e.g. “eye spots” have proven the structures actually have other functions such as courtship signals. Even then, finding the function of something never explains how the structure came about. Ref Lepidoptera, hearing, prediction

Evidence News, 26 May 2010

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