The following is an excerpt from National Geographic:
Road salt used to clear snow-covered roads in the United States is creating beefier monarch butterflies, a new study says.
A monarch butterfly rests in Minnesota. Photograph by Jim Brandenburg, Minden Pictures, Corbis
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.