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Shrinking Eyespots On Butterflies

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Y:        Wow, what a beautiful butterfly!

D:        I don’t know, I think those eyes on its wings are kind of creepy. They’re not actually looking at us, are they?

Y:        No, the spots are just a deflecting mechanism. Like a lot of butterfly species, the African satyrid butterfly’s eyespots make predators more likely to attack its wings rather than the more vital parts of its body.  

D:        Wouldn’t avoiding drawing attention to themselves be a better survival strategy?

Y:        In the dry season, yes. When it’s dry and there are a lot of dead leaves on the ground, the beige-colored butterfly can blend in easily—the only problem is they’ve got this giant eyespot on their wings that’s distinctly not leaf-like. But the African satyrid butterfly has a solution: butterflies born during the dry season have smaller eyespots that make it easier for them to blend into the leaf litter. The butterflies’ ability to shrink or expand their eyespot sizes depends on a hormone called 20E. When the season changes from wet to dry, temperatures drop, and lower temperatures lower the amount of the hormone 20E during the late larval stage of a butterfly’s development. The lower quantity of 20E affects the hormone-sensitive cells in the center of the eyespots, resulting in a smaller spot. While other species also have less 20E when temperatures are lower, this only results in smaller eyespots in the African satyrid butterfly. Scientists say the mechanism developed over millions of years in the butterfly, one small genetic change at a time.

D:        Thank goodness it took a while. I need time to get used to change.
satyrid butterfly

Satyrid butterflies have large eyes on their wings. (Wikimedia Commons)

The eyes on the wings of a butterfly can look kind of strange, but they're not looking at you, they're just a deflecting mechanism. Like a lot of butterfly species, the African satyrid butterfly's eyespots make predators more likely to attack its wings rather than the more vital parts of its body.

It might seem like it would make more sense for the butterfly to avoid drawing attention to itself alltogether, and in the dry season this is true. When it's dry and there are a lot of dead leaves on the ground, the beige-colored butterfly can blend in easily. The only problem is they've got this giant eyespot on their wings that's distinctly not leaf-like. But the African satyrid butterfly has a solution: butterflies born during the dry season have smaller eyespots that make it easier for them to blend into the leaf litter.

The butterflies' ability to shrink or expand their eyespot sizes depends on a hormone called 20E. When the season changes from wet to dry, temperatures drop, and lower temperatures lower the amount of the hormone 20E during the late larval stage of a butterfly's development.

The lower quantity of 20E affects the hormone-sensitive cells in the center of the eyespots, resulting in a smaller spot. While other species also have less 20E when temperatures are lower, this only results in smaller eyespots in the African satyrid butterfly. Scientists say the mechanism developed over millions of years in the butterfly, one small genetic change at a time.

Reviewer: Jeff Oliver, Oregon State University

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