Monarch Butterflies Migrate with a Magnetic Compass

Monarch butterflies are famous for their remarkable annual migration, traveling 2,000 miles from eastern United States to central Mexico every Autumn. Now researchers have determined that these butterflies find their way much like some birds do, using an internal magnetic compass.

A study published in the journal Nature Communications details how researchers from the University of Massachusetts and Worcester Polytechnic Institute identified the use of a light-dependent inclination magnetic compass in migrating monarchs.

"Our study shows that monarchs use a sophisticated magnetic inclination compass system for navigation similar to that used by much larger-brained migratory vertebrates such as birds and sea turtles," co-author Robert Geagear said in a statement.

His colleague and senior author Steven Reppert adds that understanding this mechanism can help researchers better protect the monarch butterfly, which has been facing declining numbers thanks to climate change and loss of fir tree groves used for wintering in Mexico.

"A new vulnerability to now consider is the potential disruption of the magnetic compass in the monarchs by human-induced electromagnetic noise," he explained.

Many migratory birds, like the European robin, face a similar problem - as described by a small-scale investigation published last month in the journal Nature - where overlapping electromagnetic frequencies in urban settings can interfere with magnetic orientation.

According to this latest butterfly study, researchers determined monarch butterflies use a similar navigation guide after observing them in a controlled setting. Using flight simulators equipped with artificial magnetic fields, the study's team determined that monarchs would orient themselves to a strong magnetic field.

Interestingly, they found that these internal magnetic compasses are light dependant, using light-sensitive molecules called cryptochromes. The molecules can detect small changes in Earth's magnetic field, and work only when exposed to light waves that can even penetrate cloud cover in invisible ultraviolet frequencies.

"[This] reveals another fascinating aspect of the monarch butterfly migratory behavior," said Reppert, who admits to having long wondered how these butterflies knew where they were going under even when the Sun was tucked away on overcast days.

The study was published in Nature Communications on June 24.