Intelligence in Nature - Jeremy Narby [45]
Arikawa and his colleagues also demonstrated in the course of their studies that the retina of the swallowtail butterfly has at least five different types of spectral receptor: ultraviolet, violet, blue, green, and red. They recently found a sixth receptor, which is broadband, and probably works as a general luminosity detector. In comparison, humans have only three types of spectral receptors: red, green, and blue. Arikawa and his colleagues concluded: âThe extremely richly endowed visual system of butterflies evidently provides these animals with a versatile information-processing apparatus.â
Astonishingly, the tiny brain of a butterfly is equipped with a system of color vision that is superior in some respects to our own.
Ultraviolet photoreceptors serve several purposes. They enable butterflies to see flowers that have pigmented ultraviolet spots indicative of nectar and pollen within. They also allow male butterflies to detect the distinctive ultraviolet stripes on the hind wings of female butterflies, which facilitates courtship and mating. Sometimes nature uses signs that human eyes cannot detect.
Butterfly visual systems develop during metamorphosis, when young butterflies are still full-grown caterpillars undergoing self-transformation in the pupa. While caterpillars have six simple eyes on each side of the head, butterflies develop an additional pair of large, compound eyes. The simple eyes of caterpillars have only three kinds of photoreceptors, while the compound eyes of butterflies have twice as many. Butterflies are transformers. They do not sprout just wings in the pupa but brand-new eyes as well.
I found Arikawaâs work fascinating, but I wondered what could drive a person to spend several decades focusing on color vision in butterflies. I asked him about it. He replied, âI am actually a color-blind person, and I have been interested in color vision processing in general. I wanted to know how the processing of color goes on in the brain and in the eyes. And I have really liked butterflies ever since my childhood. I was raised as an insect guy. My father gave me nice insect nets and took me to places where I collected butterflies and beetles.â
Arikawa said that when he was young, he had a science book for children which stated that insects in general do not see red. This was the received scientific opinion at the time. But Arikawa knew better because he had closely observed the behavior of butterflies in his parentsâ garden in Tokyo: âMy mother loved flowers, and she had lots of flowers in the garden. We had huge tiger lilies and hibiscus. And I knew that these butterflies really prefer red flowers over yellow and blue. It sounded strange to me that insects, including butterflies, cannot see red. So that is really the first point at which I became interested in the color vision system of butterflies.â
Arikawa has studied butterflies for his entire professional life. He made his first contribution to science as a graduate student, back in 1979, when he discovered that butterflies have light-sensitive neurons next to their genitals. He found that they use these âeyes,â or photoreceptors, for correct coupling between males and females, and that females also use them to confirm that they are correctly laying eggs.
Once Arikawa settled into his academic teaching position, he went on to prove that butterflies have color vision including red sensitivity. I asked, âNow that you have been studying their brains and visual systems for