14 DAY TRIAL // The fact that butterflies had ears remained a mystery to science until 1912, when the first such structures were ever identified. Since then, researchers have analyzed them on all sides, and have discovered that the organs, far from being similar in all butterfly species, were in fact extremely diverse and different. The latest insect to reveal its ears was the blue morpho butterfly (Morpho peleides), a species of butterfly that carries its listening apparatus on its wings. Scientists believe that it uses them in order to recognize the threats from incoming or nearby birds, LiveScience reports.
The tiny ears are perfectly capable of making out both high-pitch and low-pitch sounds, and it may be possible that the butterflies are actually able to identify various species of birds, if they know the noises that their wings make. Several bird species have distinct flapping sounds. The blue morpho was the last in a series of butterflies that was studied for ears. Not all species have them, but this one, which amazes people through its beautiful coloring, has its tympanal membrane located at the base of the wing. The structure resembles a yolk at the center of a fried egg, the leader of the new research, University of Bristol expert Kathleen Lucas, says.
Investigators estimate that the basic operating principle for these membranes is fairly simple. As the sounds hit them, they make them vibrate and they are thus transformed into nerve impulses by neighboring sensory organs. The impulses are then picked up by nerve cells and get delivered to the butterfly's nervous system. The scientists were very curious as to the type of frequencies the insects responded to, so they played sound waves in the 1,000- to 5,000-Hertz range, from within the estimated hearing range. Humans can hear sounds between 20 and 20,000 Hertz, while speech revolves around 100 to 4,000 Hertz.
In the experiments, it was revealed that only the sides of the membrane vibrated at low-frequency sounds, whereas, at frequencies higher than 5,000 Hertz, all of the membrane, including the dome at its center, resonated. The team found that the ears were, indeed, more inclined to hearing low-pitch noises, but examinations hint at the fact that higher sounds could be heard as well. The team admits that the idea needs more research, and that a firm conclusion has yet to be drawn.
“Not a lot of ears are able to do that [hear both high and low frequencies]. The moth ear is a simple responding ear; it listens to a certain frequency range, and it doesn't matter what frequency it is within that range, [the moth] hears it and initiates an escape response,” Lucas says. The team published its finds in the latest issue of the respected Journal of Experimental Biology.