Wildlife Conservation
3:54 pm
Tue April 22, 2014

New St. Louis Initiative Encourages Residents To Plant "Milkweeds For Monarchs"

The City of St. Louis and several partners are launching a project to help monarch butterflies.

It involves encouraging area residents to plant milkweeds -- a plant with large fruit pods that release fluffy seeds in the fall.

Monarch caterpillars rely exclusively on milkweeds for food.
Credit Lisa Francis/Missouri Botanical Garden

The Saint Louis Zoo is one of the partners in the “Milkweeds for Monarchs” initiative, along with the Missouri Botanical Garden and the Missouri Department of Conservation.

The zoo's curator of invertebrates, Edward Spevak, says milkweeds are critical to the monarch’s survival.

“Monarch caterpillars can only feed on milkweed,” Spevak said. “If you can’t feed the caterpillars, you’re not going to have adults.”

But Spevak says milkweeds have largely disappeared from the Midwestern landscape.

He says as the price of corn and soybeans has gone up, farmers have responded by planting “all the way to the fence line,” eliminating the natural areas where milkweeds used to grow. He says at the same time, the use of herbicides has increased, killing off any milkweeds growing near agricultural fields in range of drifting herbicide spray.

Without milkweeds, Spevak says what he calls the “incredible biological phenomenon” of the monarchs’ annual migration between North America and Mexico could end in less than a decade.

Spevak says monarchs pass through the St. Louis region in the spring and fall.

Their caterpillars are easy to spot. “They’re banded white and black and sort of a greenish yellow,” Spevak said. “And then they have what looks like two fleshy antennae sticking off their butt and off their head.”

The caterpillars’ dramatic coloration warns birds and other would-be predators that they are about to get a toxic mouthful. The caterpillars get their chemical protection by eating milkweeds, which contain toxins called cardenolides that the monarchs have evolved to tolerate.

The “Milkweeds for Monarchs” initiative is part Mayor Francis Slay’s “Sustainability Action Agenda” for St. Louis, which aims to foster connections between city residents and urban natural resources.

Follow Véronique LaCapra on Twitter@KWMUScience