Wing transparency helps butterflies avoid predators

A new study led by the University of Sorbonne has found that transparent wing patches in several species of butterflies and moths may have an important role in warding off predators. The wing transparency seems to have co-evolved with bright color displays in many different species.

Despite their delicate looks, butterflies and moths have many defenses, such as transparent patches on their wings that are often helping them avoid detection, or bright, contrasting colors to warn predators that they are dangerous or toxic.

The warning color patterns are so effective that other butterfly or moth species evolve to mimic them, even if they don’t have the same toxic characteristics. According to this new study, some species have evolved both vivid warning colors and transparent patches.

“We set out to explore the structural and optical features of transparent patches in various species that also have warning colorations,” said study first author Charline Pinna. “By doing so, we hoped to determine how butterflies and moths evolved these defenses and how bird predators perceive them.”

By using a method called spectrophotometry to measure the transmission of light through the transparent patches of 62 species, and computer modelling to assess how similar the patches would look to bird predators, Pinna and her colleagues have found that the transparent patches on the wings of insects and their mimics appear very similar to birds. This suggests that different species are undergoing convergent evolution, by evolving similar traits that are beneficial to their survival.

However, transparency may come at a cost, especially for species living in the humid tropics. According to the scientists, transparent patches are likely less water resistant than opaque wing patches.

Moreover, they may also have a negative effect on insects’ thermoregulation, by not allowing them to accumulate sufficient heat. Yet, since this trait has repeatedly evolved in both butterflies and moths, it seems that the benefits clearly outweighed these costs.

“Our findings show how species with transparent wing patches may benefit from double protection from predators,” concluded study co-author Marianne Elias, a senior evolutionary biologist at the Sorbonne. “At a distance, transparent patches may make butterflies and moths harder for predators to see, but up close their warning color patterns may also alert predators to leave them alone.”

The study is published in the journal eLife.  

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By Andrei Ionescu, Earth.com Staff Writer