Millions of monarch butterflies migrate through North America every year between September and November, forming massive swarms that resemble dark clouds in the sky. Scientists at the University of Massachusetts in Worcester have discovered that these butterflies use a complex inclination compass that functions based on specific wavelengths of UV light. While it was already known that monarch butterflies orient themselves based on the position of the sun, the researchers found that the Earth’s magnetic field also plays a crucial role in their navigation. The scientists conducted an experiment by placing some monarch butterflies in a special cage where they could manipulate the magnetic field and regulate the wavelengths of light. The results showed that the butterflies have an inclination compass that is dependent on UV light with wavelengths between 380 and 420 nanometers.
The monarch butterflies’ inclination compass is based on their ability to perceive the angle of the magnetic field lines relative to the Earth’s surface, known as inclination. This type of compass does not distinguish between magnetic north and south poles but rather between polar and equatorial directions. The researchers found that the butterflies’ compass is also light-dependent and only functions when exposed to UV light within a specific range of wavelengths. The basis of this compass system is likely light-sensitive magnetic sensors in the butterflies’ antennae. When the researchers painted these sensors black, the butterflies’ inclination compass no longer functioned.
This discovery sheds new light on the remarkable navigational abilities of monarch butterflies and how they are able to find their way to their wintering grounds in central Mexico, even when the sun is obscured by clouds. The researchers’ findings were published in the journal Nature Communications, and they hope that further research will help us better understand the mechanisms behind the monarch butterflies’ remarkable migration.
