Based on a study recently published in Cell Reports, scientists think they now know how monarch butterflies determine the southwest direction they fly each fall as they migrate to Mexico from the U.S.A. and Canada. The study determined that the monarchs have an internal, genetically encoded compass. Here’s how it works.
We know from from previous research that the monarch butterfly has the ability to integrate the time of day and the sun’s position on the horizon. The big question tackled by this recent research was how this clock and the sun’s position work together to direct the monarch’s flight behavior.
Monarchs, like most animals, have an internal clock as part of their genetic make-up. This circadian clock is housed in the monarch’s antennae. They keep track of the sun with their large, complex eyes. Then they combine this information with the sun’s position in the sky and somehow know the direction to travel.
Basing their study on the southwest flight in the fall, researchers found that monarchs make course corrections but not necessarily the shortest distance to get back on course. They discovered there is a separation point that controls whether the monarch turns right or left to make course corrections — it will turn whichever direction doesn’t require it to cross the separation point.
Each year, monarchs migrate more than 2,000 miles back and forth between Canada and central Mexico, so the assumption is that the information about the clock, the sun’s position and the separation point work the same way in both directions.