Orientation by Magnetic Dip

Monarch Butterfly

Monarch Butterfly

The earth has a magnetic field with the North and South magnetic poles as the axis of the magnet. The magnetic lines of force emanate from the South Pole and return to earth. The lines intersect the earth at -90 degrees at the magnetic South Pole and +90 degrees at the magnetic North Pole. The magnetic dip varies from -90 degrees to + 90 degrees at points in between the magnetic poles. Magnetic dip, first described by German scientist Georg Harmann in the mid 1500s, is an indication of latitude and can be used in navigation.

It can be shown experimentally that fall migrating monarchs can use magnetic dip to orient south. The monarch magnetic compass only functions in the presence of UV/blue light suggesting that the light-sensitive cryptochorme is needed. The details of magnetic navigation in Monarchs is sketchy, but may be important in guiding monarchs to their primary overwintering site in Mexico.

About jjneal

Jonathan Neal is an Associate Professor of Entomology at Purdue University and author of the textbook, Living With Insects (2010). This blog is a forum to communicate about the intersection of insects with people and policy. This is a personal blog. The opinions and materials posted here are those of the author and are in no way connected with those of my employer.
This entry was posted in behavior, by jjneal, Environment. Bookmark the permalink.

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