The monarch butterfly uses a magnetic compass to guide its extraordinary migration thousands of km across North America, scientists say.
Monarchs are known to possess a Sun compass but even on cloudy days they still keep flying south towards Mexico.
In a laboratory experiment, butterflies changed direction when the magnetic field around them was altered.
It suggests that like turtles and birds the insects have a geomagnetic compass, says a study in Nature Communications.
It raises concerns the butterflies may be disturbed by human-induced magnetic "noise" - which can apparently disrupt the European robin, a migratory bird.
Miracle migration
The North American monarch butterfly Danaus plexippus is famous for its epic journey from Canada to Mexico.
Every Autumn, despite never having flown more than a few hundred metres, millions of the insects set off across Lake Erie and head south for the warmer forests of the Michoacan mountains.
There they spend the winter - coating the trees in an amazing display which attracts thousands of tourists.
The ancient Mayans believed the butterflies were the souls of the dead, and the insect has become a symbol of North American trade and cooperation.
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