When snow melts, road salt runs into nearby soil and into the roots of common plants, which are in turn ingested by caterpillars. Then, as they become adult butterflies, their brains and muscles develop abnormally: The females develop larger eyes and brains, and males develop more muscle.
These are potentially positive changes, as they aid the butterflies in elements of mating and reproduction. Larger muscles help males fly longer and farther, enabling them to find more mates. Larger eyes allow the females to seek out better plants on which to lay their eggs.
Just like in people, sodium is good for butterflies in low quantities: Itâ€™s one of most important elements of muscle and brain development.
But thereâ€™s a catch: â€œAs [the salt] increases a little bit, thatâ€™s probably a good thing for them,â€ saidÂ study co-author Emilie Snell-Rood, a biologistÂ at the University of Minnesota.Â â€œAs it increases even more, it becomes toxic and stressful.â€