Butterflies are becoming more mobile. According to an article on BBC News, monarch butterflies have evolved for longer flights, with wingspans up to 20 percent larger than their more stationary brethren. The butterflies migrate between Mexico, the U.S. and Canada in search of warm temperatures. According to University of Georgia professor Sonia Altizer, "Large, elongated wings are better for monarchs that undertake long-distance flights."
The monarchs are not the first species to show evolutionary changes for long distance travel. According to the BBC, many species develop longer wings for extended migration. What is unique about these butterflies changes is that some monarchs have grown the longer wings while others have not. Altizer explains that some of the monarchs live in tropical locations like the Caribbean and have no need to migrate.
Altizer and her team bred butterflies to "show that large wings were inherited, having a genetic basis, rather than being produced by butterflies in response to environmental factors" like warm weather. Altizer says this is further proof that evolution is behind the large wings. Next steps for the researchers include exploring differences in East and West Coast butterflies in relation to soaring or gliding flights to determine how much the wing size "improves the flight performance."