Great Migrations Butterflies (National Geographic Kids Readers, Level 3) eBook

Each year, as the weather gets colder, monarch butterflies make a mass migration to their winter homes. For them, this trip means life or death. As the air cools, butterflies have a hard time flying. Below 55 degrees farenheit, their wings stiffen making it harder for them to fly long distances. Below 40, their wings paralyze completely.