Buckeyes (Junonia coenia) are the most common butterflies feeding on our decomposing apples.
Wing eyespots are common on butterflies. Their role is controversial, though many experiments indicate eyespots are used defensively in many species that feed on fermenting fruit. The idea is that insects flash the eyespot pattern at potential predators, who are startled by the sudden appearance of what appears to be the face of a potential predator, and then move quickly to find easier prey in a safer location.
The line of reasoning continues with determination that this function is most useful in species that feed on fermenting fruit. Fermentation produces alcohol, which leads to inebriation and slow defensive response time in those decomposing fruit-feeding species.
I decided to follow this up at home using remnants of fruit from our excessively producing golden delicious apple trees. I stepped on a few of the decomposing apples the previous day, and went out the following afternoon to photograph species attracted to the decomposing fruit and observe notable behaviors.
Flies, butterflies and honeybees were the predominant insects encountered. Interestingly, all of the butterfly species feeding on the fermenting fruit had wingspots. Most rhythmically opened and closed their wings while feeding.
About fifteen minutes into my photographing my wife let the dogs out, who of course were intent on seeing what I was photographing. In each case I observed, feeding butterflies approached the dogs face on and flashed their wings open several times. If the dogs continued in their direction, the butterflies flew off, albeit somewhat slowly.
No experiment, but a consistent observation…
Classic defensive posture? I was behind this buckeye as one of our dogs approached from the opposite direction.
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Things Biological 