How Do Butterflies Navigate ?

Every autumn Monarch butterflies make their way from the northern US to Mexico where they spend the winter. But how do they know which direction to fly ? To find out researchers Henrik Mouritsen and Barrie Frost from Queen's University Ontario found that in the sunshine the butterflies headed southwest. But if the butterflies were 'jet-lagged' for 6 hours first they headed off 90 degrees off-course. The researchers suggest that they must be using some kind of Sun-compass linked to their body clock. Butterflies developing larger muscles as changing weather forces them to fly further.