ST. LOUIS (KSDK) - You can do something simple to save the threatened monarch butterfly this spring: plant milkweed.

It's part of a city of St. Louis initiative that encourages private butterfly gardens to plant milkweed. Monarch butterflies only lay their eggs on milkweed, and it's also the only thing that caterpillars eat. When host plants are scarce, so are butterflies.

Mayor Francis Slay was on-hand Tuesday to plant milkweeds at Brightside St. Lois Demonstration Garden for Earth Day.

It's part of the city's sustainability plan, a 260-page document with the overall goal of making the city more environmentally friendly.

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