The Butterfly Changes its Spots — Eyespots, that is
Eyespots are one of nature’s favorite forms of misdirection, shared by fish, frogs, birds, and many insects. Aside from deflecting attack, they can also be used as a “startle” mechanism, being flashed just long enough to delay attack briefly and allow a species to escape. In addition, they can also be used for camouflage, providing protection by making an animal less detectable.
Recent research has shown that one species of butterfly, Bycyclus anyana, uses eyespots in two different ways. The study, published in Proceedings of the Royal Society B, shows that B. anyana changes the color and intensity of its eyespots according to the season and the types of predator it is likely to face.
Bycyclus anyana produces about five generations a year during both wet and dry seasons in its native habitat. Through a process scientists call “phenotypic plasticity,” the same genes can produce two different eyespot patterns in the adults. Warm temperatures of the wet season create large and bright eyespots, while cool temperatures common in the dry season produce dull and small eyespots.
During the wet season, predatory insects such as praying mantids are their greatest enemy, and the butterflies’ large eyespots make colorful targets for attack, sort of like a matador waving a cape to distract a charging bull into attacking the wrong thing. The showy eyespots cause the mantids to attack a butterfly’s wings instead of the more vulnerable body or head. The wings are badly damaged, but the insect can escape and live to reproduce, as the following video shows.
“Having the right type of eyespot in the right season allowed the butterflies to live long enough to lay eggs and have more offspring in the next generation,” said Katy Prudic, lead author of the study and a researcher with the Department of Integrative Biology in the College of Science at Oregon State University. “With the wrong eyespot at the wrong time, they were quickly annihilated by the mantids.”
However, during the dry season, most mantids and other insect predators are dead, but birds abound and the butteflies change their spots accordingly. Instead of using large, colorful eyespots to deflect attacks, they instead sport small, dull eyespots which makes them more difficult to detect.
“Color pattern has always been a form of protection against predators in nature,” Prudic said. “It can take the form of camouflage, mimicry, delaying or redirecting attacks. But studies that observed and hypothesized about such changes have been difficult to document in controlled experiments such as this.”
Read more at: