Science has found that there are a record number of photoreceptors in the eye of the butterfly.
Researchers studied the eyes of the Common Bluebottle which is a species of butterfly. They got quite a shock. Besides the large eyes, these butterflies use their shiny colorful wings to visually communicate stuff.
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Their vision is very acute. What was unexpected was that the Common Bluebottles have over 15 different types of photoreceptors. These resemble the rods and cones in the human eye. Before this, no more than 9 such photoreceptors have been found in any insect species.
Color vision has been studied in many species of insects before. The number of photoreceptors differs from species to species. The presence of 15 varieties in a single species was a remarkable discovery.
The great number of photoreceptors is a necessity. It is with their aid that the butterflies can see various colors. Each one is stimulated by a certain type of wavelength and not by others.
The brain of the butterfly is able to differentiate between colors based upon the information coming from each photoreceptor.
"We have studied color vision in many insects for many years, and we knew that the number of photoreceptors varies greatly from species to species. But this discovery of 15 classes in one eye was really stunning," says Kentaro Arikawa, Professor of Biology at Sokendai (the Graduate University for Advanced Studies), Hayama, Japan and lead author of the study.
Through various experiments that got carried out, it was found that these photoreceptors are stimulated by UV light, violet, blue (three are affected by it), blue-green, green light (four are affected by it) and red (five are affected by it).
The legitimate question is why Bluebottles require so many photoreceptors. Human beings have only three classes of cones and are able to sense millions of colors.
Other insects too have just a few photoreceptors and they too have excellent color vision. Common Bluebottles tend to use four photoreceptors for ordinary color vision.
The others are used to detect various stimuli in the environment. These include flitting objects in the sky. Also colorful things concealed in the verdure are detected by the other photoreceptors.
Another species of butterfly also shows a similar mechanism in its vision strategy. This one has six photoreceptors.
While butterflies have lower visual acuteness than humans, they do have an advantage in another regard. Their visual field is very expansive. They can also pursue fast moving objects with dead certainty.
They are able to differentiate UV light and polarized light. To imagine how they see the world is an exciting field of endeavor for human beings.
"Butterflies may have a slightly lower visual acuity than ourselves, but in many respects they enjoy a clear advantage over us: they have a very large visual field, a superior ability to pursue fast-moving objects and can even distinguish ultraviolet and polarized light. Isn't it fascinating to imagine how these butterflies see their world?" says Arikawa.
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The results of this study are published in the open-access journal Frontiers in Ecology and Evolution.