Jim Gilbert's Journal

September 11, 1998

     Monarchs Migrating

We see them between May and October but it's in late summer, when their population is the greatest and migration has begun, that we are most aware of the monarch butterfly, a wonder of the insect world.

Monarchs travel individually, not in flocks. When hundreds or even thousands are seen flying together, it's probably because of the sudden departure from a roosting location where they have spent the night during migration.

In migration, monarchs save energy by riding thermals, or rising air masses, which lift them to favorable altitudes. Their soaring skills are so efficient that many arrive in Mexico fat and healthy, having gained--not lost--weight on the trip.

Monarchs fly anywhere from ground level up to 7,000 feet, the cruising altitude of many light airplanes. Traces of the mineral magnetite, the same material used in our compass needles, are found in monarch butterflies. The magnetite may explain some of the monarch's navigational abilities.