In addition to the sun, they also use the earth's magnetic field as a reference. Butterflies fly every year from the USA to Mexico's mountains.
US monarch butterflies use the sun and the earth's magnetic field as navigation tools for their famous long-distance migration.
Flapping its delicate orange and black wings, the insect travels thousands of miles each year from the United States and southern Canada to the Michoacan Mountains in central Mexico where they spend the winter.
Butterflies, whose scientific name is Danaus plexippus, are known to use a type of solar compass on the brain.
Interestingly, however, they are also able to migrate when the sky is cloudy, suggesting a codependency on a magnetic compass.
Massachusetts biologists now say they have found evidence of this, which makes the butterfly the first long-distance migratory insect to use magnetic navigation.
The scientists placed the monarchs in a flight simulator, which they surrounded with different artificial magnetic fields to test the insects' sense of direction.
Most oriented toward Ecuador in the initial test, but turned north when the inclination angle of the magnetic field was changed. The compass worked only in the presence of light at the upper end of the visible light spectrum.
According to the researchers, the butterfly antennae seemed to contain light-sensitive magnetic sensors to do all the work.
The research, published in the journal Nature Communications, includes the monarch to a growing list of birds, reptiles, amphibians, turtles and insects, including bees and termites, which are believed to use the magnetic field for navigation.
"Our study reveals another fascinating aspect of monarch butterfly migratory behavior," the authors stated.
"Increased knowledge of the mechanisms underlying the decline in migration may help preserve it, which is currently threatened by climate change and the continued loss of plants from the Asclepian family and hibernation habitats," says a study.
Another vulnerability to consider is the potential disruption of the magnetic compass in monarchs by man-induced electromagnetic noise, which may apparently affect the geomagnetic orientation of a migratory bird.