The Monarch Butterflies

A Monarch butterfly arrives in Mexico during November after flying from Canada to their sanctuary near Valle de Bravo, Mexico, Thursday, Nov. 28, 2002. (AP Photo/Marco Ugarte) | ASSOCIATED PRESS. A new study suggests that monarch butterflies use an internal magnetic compass to help navigate on their annual migrations from North America to central Mexico.

Scientists already knew they navigate by the sun. But the insects do just fine on very cloudy days, leading to suspicions they also use a magnetic compass, like migratory birds and sea turtles. 

Previous studies haven’t made a clear case for that, according to authors of the new study, from the University of Massachusetts Medical School in Worcester and the Worcester Polytechnic Institute.

They tethered monarchs in a chamber without any outdoor light and showed that their flight patterns responded to changes in the magnetic field. Further work suggested the compass is in the antennae.

Millions of the black-and-orange butterflies spend the winter in Mexico.

The new work was released Tuesday by the journal Nature Communications.