Large orange butterflies have been heading south through Kansas these last few weeks. They are monarch butterflies. This migration continues until the weather becomes cold.
Most local butterflies and moths have adapted to Kansas winters by laying eggs or overwintering in a cocoon or chrysalis stage. But monarch butterflies never evolved the cold-hardiness to survive harsh North American winters.
Populations on the West Coast migrate down to Pacific Grove, California, where they survive in milder conditions. East of the Rocky Mountains, our monarch butterflies are heading south by southwest into Mexico where they will overwinter on the hillsides of a few mountains. Their numbers will be so great that some tree limbs will break.
Monarch butterfly caterpillars feed on milkweed. The white sap that oozes from many milkweed stems contains a heart poison that seriously affects vertebrates. Very few animals can feed on milkweed without getting sick. However, monarchs are not harmed by these toxins. Not only are they one of a few insects that can eat milkweed, they keep the poisonous compound in their wings and outer exoskeletons, making monarch larvae and adult butterflies toxic to birds and other predators.
Instead of their caterpillars being green to hide from birds, they are brightly striped to advertise their bad taste. And the adults are likewise attractively bright orange. Once a young inexperienced bird tries to eat a monarch, it immediately vomits it back up. The bird has learned to leave the striped caterpillars and big orange butterflies alone.
Monarch butterfly development from egg to adult takes about 30 days. Therefore in the spring, the monarchs that move north and lay eggs in the southern U.S. will go through several generations. Those that make it to Canada will have a shorter time to cycle before fall signals it is time for their trip south.
Adult monarchs no longer grow, but they need to fuel their flight south to Mexico. Flower nectar is about 20 percent sugar and monarchs will visit many different flowers. They locate flowers by sight but use taste receptors on their feet to find the nectar.
During the summer, adults live for 2 to 5 weeks during which they mate and lay eggs. But the last generation that emerges in late summer or early fall must migrate to their overwintering grounds and will live for 8 or 9 months.
Research on monarch migration was conducted by the late Professor Lincoln Brower (September 10, 1931 – July 17, 2018) who marked monarch butterflies and then tried to trace their migration and estimate population numbers from recaptures. However, the migration was so large and the marked individuals so few that this was a difficult task.
It was Dr. Orley Taylor of the University of Kansas who expanded the research. Having worked on other butterfly research as well as the African honey bee problem, Dr. Taylor turned to the monarch migration puzzle. He enlisted school children and other members of the public nationwide in a massive tagging effort. By enlisting the aid of “citizen scientists,” it is possible to secure better estimates of the monarch population and the factors that influence its migration.
This data could not come at a better time, because the monarch migration appears to be declining in the long term. Many factors may be involved, but the use of herbicidal chemicals in the central United States has produced massive strips of farmland with beautiful crops and absolutely no weeds—including milkweed.
Monarch Watch is Dr. Taylor’s organization based at K.U. It is not only command central for receiving nationwide data on tagged monarch butterflies, but is involved in helping the public grow milkweed gardens and appreciate the need to leave some portion of roadsides uncut.
“Biology of the Monarch Butterfly” authored by Dr. Taylor is a Kansas School Naturalist issue available free upon request. It is also accessible online at www.emporia.edu/ksn and is available in print in Spanish as well. There is a lot more to learn about these beautiful butterflies flying south right now.
John Richard Schrock is a professor at Emporia State University.