How do butterflies know the way to Mexico? For years, scientists have thought that monarchs use the sun to calculate their position, but now a new study suggests they’re also wired up with a magnetic compass, BBC reports. To test the idea, researchers placed the butterflies in a special flight simulator where researchers could control the magnetic fields within. They found that as they altered the fields, the butterflies would change the direction of their flight to the newly defined south. The study is described this week in Nature Communications.