Butterflies are toughening up and getting bigger muscles, brains, and eyes—but the changes aren’t natural. Scientists have discovered that the salt that thaws streets is seeping into roadside plants that caterpillars consume and making them brawny, National Geographic reports. A key substance for muscle and brain growth, sodium causes abnormalities that help the insects see better and fly for longer periods of time, but there’s a catch: It can be deadly. The study, published online this week in the Proceedings of the National Academy of Sciences, found that caterpillars with normal diets have a 58% survival rate, whereas those that consume sodium-enriched plants have a 40% survival rate.
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