Butterflies employ a compass during migration

Scientists at the University of Massachusetts (UMass) Medical School and Worcester Polytechnic Institute have added further clarification to the complicated process of butterfly migration.

The research, published in Nature Communications, said that monarch butterflies use a light-dependent, inclination magnetic compass to help them guide their way during migration. 

Every year millions of monarch butterflies use a sophisticated navigation system to make sure their 2,000-mile journey takes them in the right direction. This takes them from breeding sites in the eastern United States to their appropriate winter habitat in central Mexico. 

Senior study author Professor Steven Reppert, the Higgins Family Professor of Neuroscience and distinguished professor of neurobiology at UMass Medical School, said the study reveals another fascinating aspect of the monarch butterfly migratory behaviour.

"Greater knowledge of the mechanisms underlying the fall migration may well aid in its preservation, currently threatened by climate change and by the continuing loss of milkweed and overwintering habitats. A new vulnerability to now consider is the potential disruption of the magnetic compass in the monarchs by human-induced electromagnetic noise, which can also affect geomagnetic orientation in migratory birds." added Professor Reppert.

Co-author Robert Gegear, PhD, assistant professor of biology and biotechnology at WPI, said the study shows that monarch butterflies use a sophisticated magnetic inclination compass system that is similar to the one that birds and sea turtles use.

It is thought that this compass is used when daylight isn't enough, such as in dense cloud cover, to help them navigate when visual cues are unavailable.

This is the first study that has accounted for the possibility that the magnetic compass was influenced by ultraviolet light that can penetrate cloud cover, as previous research negated this and resulted in conflicting or unconvincing answers 

Given the ability of monarch cryptochromes (CRY) to restore a light-dependent magnetic response in CRY-deficient Drosophila, Professor Reppert and colleagues suspected that monarchs also possessed a light-dependent magnetic compass, which was then proven in further tests.