Monarch butterflies have always been remarkably resilient. Every fall, these delicate orange-and-black travelers set out on a journey so improbable it borders on myth, flying some three thousand kilometers from Canadian fields all the way to Mexico's mountain forests, their overwintering grounds. They've been weathering habitat loss, extreme weather and pesticides, but new research from the University of Ottawa suggests a new snag in their epic trek. The culprit? Nectar. Turns out, their main food source isn't what it used to be.
