Monarchs and Milkweed

A monarch on milkweed.

A female monarch butterfly wriggles out of her cocoon and spreads her wings into the warm sun on an Ontario afternoon. Soon, she will join millions of her kind in a magnificent migration that traverses the continental U.S. to avoid a freezing winter.

Those summering east of the Rockies fly to a specific central Mexican forest. West of that mountain range, monarchs migrate to two spots along the California coast. Either way, the journeys are arduous and as long as 3,000 miles. In spring, these same butterflies begin the return trip, but only make it as far as Northern Mexico or the Southern U.S., where they lay eggs on milkweed and die.

Populations of monarch butterflies are, however, in a precipitous decline. Their numbers have dropped as much as 90% since the 1990s. Factors such as hurricanes and weather extremes have taken their toll, but more critical has been the loss of milkweed—the only plant on which monarch butterflies will lay their eggs and their caterpillars will feed.

Development, mowed roadsides and increased chemical interventions mean that milkweed populations have declined. Some estimates have that decrease as high as 21% in the U.S.

Adults overwinter en masse.

Several organizations have mobilized to help stem the tide. Groups such as Monarch Waystation, a program of monarchwatch.org, encourages gardeners to help by, among other things, planting milkweed. Farmers, too, are helping.

Assisted by a farming practice called STRIPS (Science-based Trials of Rowcrops Integrated with Prairie Strips), many producers have begun to re-introduce native plants. Says Dr. Mary Harris, adjunct professor in Natural Resource Ecology and Management at Iowa State University: “Native tallgrass prairie vegetation is planted within a row-crop field. Milkweeds are included in the mix, and in addition to all the flowers providing nectar for butterflies and bees [200-plus species of native bees, not honeybees], and pollen for bees, these strips provide habitat for grassland birds.”

Harris adds that there is a more direct benefit for the farmer too. “From these strips, you get disproportionate benefits in the form of tremendous reductions in sediment and nutrients moving out of the field.” (Please note: Milkweed can harm grazing livestock, so it is best to keep such plants out of the pasture.)

The good news is that monarchs can still rebound, but help is needed now. It is reported that 2014 was a pretty good year for the butterflies, but the number overwintering will not be estimated until after this article goes to press. Simply put: They aren’t out of the woods yet … pun intended.