ST. LOUIS – Migratory monarch butterflies recently passed one year on the endangered species list and, with their numbers decreasing, seasonal monarch migration could become a rare sight.

Cooling temperatures and shortening days are the environmental cues that trigger monarchs to migrate ahead of the freezing weather. They’ll travel from Canada to Central Mexico, where they’ll spend the winter.

Chris Hartley, the science education coordinator at the Butterfly House, says we’ll be seeing an increase of monarchs over the next few weeks but the North American population is threatened.

“There are monarchs in Central America, in Southeast Asia. Same species of butterfly, but the North American population right here, where we live in Missouri, is the one that migrates. That is a unique behavior. And that population of monarchs we have seen decline in numbers over the past several decades,” Hartley said.

The reason for the decline is broadly due to habitat loss both here and in Mexico.

“The habitat loss here is the loss of milkweed, which is the only plant they can lay eggs on. And nectar plants, which sustain them as they’re heading south. The habitat loss in Mexico has to do with the trees that they spend the winter on,” he said.

To support the monarchs on their trip, choose plants that bloom in September or October that can fuel them as they’re flying south.

“Monarchs’ favorite plants are nectar-producing native perennials. Astors, goldenrod, iron weeds. There are many good choices home gardeners can use,” Hartley said.

These plants also support bees and other native butterflies.

“Really, you are supporting the community of local pollinators and local insects that all are threatened when habitat loss occurs. So, you really are supporting a community,” he said.

And fueling the North American monarchs so that future generations can enjoy the seasonal migration of these iconic insects.

“Monarchs in the rest of the world don’t do that. They don’t need to do that. So it’s really a wonderful thing that we wouldn’t want to be lost,” said Hartley.