Butterflies' long migration hits Kansas in September.

This month brings an especially colorful spectacle to Kansas, as masses of migrating monarch butterflies pass through the state. This familiar species has migratory behavior much like that of birds, which is unique in the insect kingdom. Navigating strictly on instinct, every monarch east of the Rocky Mountains navigates toward a limited area of central Mexico to spend the winter.

Several generations separate the southward-migrating monarchs from those that went south the previous year, so they do not have elders to show them the way. The monarchs that live north of Kansas begin moving south in late August. The trigger for their trek south is thought to be the declining angle of the sun as the days get shorter, and this "sun compass" also guides them as they travel.

As the migrating monarchs progress south, local monarchs join them, making the group larger. The observed peak for the Topeka-Kansas City area typically falls around Sept. 22. The peak for the Wichita area is usually around Sept. 27. On the right day in the right location, careful observers may see hundreds or even thousands of monarchs moving in a south-southwesterly direction on their journey to Mexico. During resting periods, tree branches may be so loaded with monarchs that branches bow and appear almost completely orange.

Monarch movement is strongly affected by prevailing weather patterns, so every year may take them on a different route. A good way to attract monarchs and help them refuel on their fall migration is to have September-blooming plants around home. Asters, sunflowers, goldenrod, and sedum have blossoms to provide the nectar they need.

The right habitat nearby may even attract overnight roosts of monarchs. They cease flying in the evening and look for sheltered sites in trees to cluster together for the night. These sites typically have an easterly exposure, so the monarchs can warm up quickly in the morning sun and resume their migration. These overnight roosts are, in miniature, just like what may be seen at their over-wintering site in Mexico, where acres of trees are so blanketed with butterflies that the branches of the trees bend low with their weight.

Monarchs head back north again in March, but they are seldom the same ones that went south the previous September. Rather it is the first generation of their descendants, and they begin arriving around the second week of April. Because the spring flight north is a dispersal with the purpose of laying eggs on newly emerging milkweed rather than the mass retreat from winter that occurs in the fall, large numbers of monarchs are not seen in spring.

For more information on monarch butterflies and their amazing migration, visit the University of Kansas Monarch Watch website. To find locations to look for monarchs and other Kansas wildlife, visit the Natural Kansas website, or contact Jim Mason at the Great Plains Nature Center (316-683-5499).