Deaf Butterflies Develop Ears -
A Little Bit of Trivia
by Hazel Inglis
HearingCenterOnline.com Staff writer
The discovery of microscopic ears on the wings of a group of butterflies has shed new light on the evolutionary development of modern-day butterflies.
Our five senses are nature's gift for survival. We rely on our senses for many things. Each one gives us information about the world around us. The more information we have, the clearer the picture. Missing one or more of these senses, doesn't mean that we are helpless, just that we must rely on our other senses a little more.
One of the most important things our senses do is to alert us of dangers. Our sense of smell can help us to detect noxious gases in the air. A bitter or sour taste can be a warning that our food may be poisonous. Probing with our fingers (carefully, we hope) can alert us of sharp or hot objects. Our eyes and our ears are excellent tools to tell us when something or someone is approaching.
With this in mind, it is not surprising that researchers have discovered a group of nocturnal butterflies (Hedyloidea) that have developed ears on their wings to help escape the hungry, predacious jaws of bats.
In the article "Ultrasonic hearing in nocturnal butterflies," (January 20 issue of Nature), Dr Jayne Yack, of Carleton University and Professor James Fullard from the University of Toronto suggest that butterflies were "invented" by bats. They argue the "selection pressure" bats placed on butterflies and moths, more than 50 million years ago, forced them to evolve either daytime existence or the ability to hear a bats echo-location signal.
Until recently most butterflies were considered "diurnal", meaning, alert during the day and it was thought only moths had the ability to hear. Scientists now believe the Hedyloidea are closely related to and quite feasibly "living ancestors' of two other groups of modern-day butterflies (the Papilionoidea and Hesperoidea).
Yack and Fullard made comparative studies of the Hedyloidea, discovering that existence of ears on these insects are common among the nearly 40 species from this butterfly group. In particular they examined the anatomy of the ear from the Macrosoma Heliconiaria, a butterfly found on Barro Colorado Island, Panama.
The structure of the butterfly's ears is intriguing. Comparisons can be made to the external portion (pinna) of a rabbits ear and to the internal components of the "frequency - discriminating ears of grasshoppers." The butterfly's ear moves with its wing, which helps it to locate the origin of sounds while in flight. (Just picture having your ears on your hands, or eyes in the back of your head, and imagine how much more you could see or hear--remember this is a metaphor not a scientific analogy).
Yack and Fullard predicted that because this type of butterfly (hedylids) are nocturnal and would therefore encounter bats, they should have "ultrasound-sensitive ears and exhibit bat-avoidance behaviour." They were not disappointed. When the butterflies were exposed to an ultrasonic simulation of the echo-location sounds of bats, the insects responded by making steep dives, climbs, loops, and horizontal sweeps at a substantial increase in speed (400%)to escape their "pursuing" predator. This defense mechanism has allowed these species of butterflies to avoid being over-hunted by the bats. Unlike their daytime cousins, they remain creatures of the night.
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