The Eyes Have It

Buckeye

Buckeye butterfly Insets: Close up of some of the eyespots.

Many species of butterfly, especially in the family Nymphalidae have markings on the wings that resemble eyes. For humans, eyes, or images resembling eyes attract the attention of our brains. Movements of the face and eyes are important visual cues in human communications and interactions. Since eyes and eyespots draw our attention, it is not surprising that the subject of eyespots on the wings of butterflies has the attention of scientists.

Speculation about a “function” for eyespots dates back at least to the 1890 book edited by EB Poulton, The Colours of Animals. The book contains the speculative chapter, “Colors and markings which direct the attention of an enemy to some non-vital part, but which are not attended by unpleasant qualities”. Poulton suggested that eyespots on the wings of butterflies and on other animals could redirect the attack of predators away from vital parts (such as the head an body of a butterfly) and toward the eyespots present on non-vital portions of the wings.

Other speculations suggest that the eyespots are a form of mimicry, the eyespots “intimidating” predators because of their resemblance to the eyes of animals that are much larger and more dangerous. In some species, the eyespots are hidden during rest and flashed at a predator when the insect is disturbed. This has been interpreted as a potential defense to “startle” a predator to give the prey time to escape. Yet other evidence finds a role for eyespots in mate recognition. Perhaps eyespots have little to do with repelling predators and more to do with attracting mates?

Eyespots come in a wide variety of sizes, shapes and numbers. It is quite possible that eyespots have a range of functions that is context dependent. Perhaps the effect is large on some predators but not others. Perhaps small eyespots are better at redirecting the attack and large eyespots are better at intimidating the predator? The speculation is endless and experimentation with predators and fast flying prey is difficult to conduct. Sorting out the many speculations is likely to be a long process.

This year, 2107  buckeyes can be commonly found.  Look for them on flowers or collecting at puddles or wet spots on wood chip trails.

About jjneal

Jonathan Neal is an Associate Professor of Entomology at Purdue University and author of the textbook, Living With Insects (2010). This blog is a forum to communicate about the intersection of insects with people and policy. This is a personal blog. The opinions and materials posted here are those of the author and are in no way connected with those of my employer.
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