Monarch butterflies really are
beautiful and
cool in many ways. One ability which is helpful in their
travels is to use the
earth's magnetic field for
navigation. This comes in handy on
cloudy days and their
schedule still calls for some serious mileage
north or
south. For all practical purposes they have a little
compass built in somewhere in their bodies.
Ref: J.A. Etheredge et al (1999) "Monarch butterflies ( Danaus plexippus L.) use a magnetic compass for navigation" Proceedings of the National Academy of Sciences, vol 96, no 24, pp 13845-6.