Those wonderful orange-and-black butterflies that we love so much. They fly overhead this time of year, and we know they are headed to their overwintering sites outside of Mexico City.
But how do they get there?
Plenty of studies have been done throughout the years to try to figure out how a brain the size of a pinhead can help a monarch complete such an amazing trek, and it turns out there are multiple ways that a monarch butterfly navigates.
First, monarch butterflies have a circadian rhythm that helps them know what time it is. Think about when you wake up, you can probably guess pretty close to what time it is before glancing at your phone. Or you look outside, and the position of the sun will help you figure out the time, even without a clock.
Monarch butterflies also utilizing that innate sense of time as well as the sun’s position to orient themselves in a southwestern direction.
This circadian rhythm — a 24-hour cycle that occurs even in the absence of light — was proven in a University of Massachusetts Medical School study in which monarchs that had a normal circadian rhythm, with light from 7 a.m.-7 p.m. flew in a southwesterly direction. Monarchs that were exposed to light from 1 a.m.-1 p.m. flew southeast, because their sense of time was off and they followed the sun’s position incorrectly. Butterflies that were exposed to 24-hour light during the study flew directly toward the sun, proving their circadian rhythm was completely upset.
However, on cloudy days, monarch butterflies can’t use the sun’s position to help them. On those days, they use the earth’s magnetic pull to tell which direction is south. Geomagnetic cues help them fly toward the equator, and those magnetic receptors have been found to be in the butterflies’ antennae.
Another study found that monarchs whose antennae have been painted black couldn’t find south, meaning their antennal reception is even more important than their circadian rhythm and use of the sun. Even the butterflies who could see light but couldn’t use their antennae got lost.
Many people have seen monarch butterflies roost overnight in trees outside their homes. Year after year, groups of monarchs will spend the night in the same tree. It takes four-six generations of monarchs to migrate to the northern-most point every year, and still, that many generations later, the butterflies end up on the same trees.
No one knows exactly how that happens.
Like much in nature, the intricacies of the monarch butterfly are so incredible that humans haven’t quite been able to figure out exactly how they do what they do.
And that’s part of what makes them so amazing.