Researchers were aware that monarch butterflies navigate by the sun. Continuation of navigation even during cloudy days led to suspicion among researchers that the butterflies might also be using a magnetic compass like other migratory birds and sea turtles.

Now, scientists suggest that monarch butterflies use an internal magnetic compass to navigate through their 2,000-mile migrations to central Mexico. Researchers from the University of Massachusetts Medical School and Worcester Polytechnic Institute put monarch butterflies in a chamber with no outdoor light.

Researchers noted monarch butterflies' flight patterns act as per changes in the magnetic field. It is even suggested that the compass is in their antennae.

For past few years, researchers have remained confused as to how the North American yellow-and-black monarch butterflies that migrate every winter from southern Canada to central Mexico travel thousands of kilometres without getting lost. These butterflies travel such long distances in search of milkweed to lay its eggs.

Lately, the butterfly is quite in news due to its declining numbers. Earth's Magnetic field lines emerge from the South Pole and then re-enter at the North Pole. The field lines meet earth's surface at a particular angle called inclination angle.

Researchers noticed that the butterflies in the experimental set-up were orienting themselves as per the inclination angle, especially in cloudy conditions. It was found that monarch butterflies' antennae have proteins called CRY. The protein activates the inclination compass when light of particular wavelength fell on it.

"The defined spectral requirement for the inclination compass discovered in our studies potentially explains why previous light simulator studies were unable to identify an inclination magnetic compass", said study authors.