I let the milkweeds grow in the back of my garden to provide habitat for monarch butterflies. Jodi Henke, radio editor for Living the Country Life, brought some milkweed pods to the office last week so everyone could let the seeds grow on their property. The butterflies lay eggs on the leaves.
Habitat projects are designed to benefit a wide range of wildlife species. Pheasants Forever used to focus on birds, but is now promoting its habitat projects for bees and butterflies, as well. Here is a video that explains The Life History of Monarch Butterflies
If you have been pulling "weeds" in your landscape that can help wildlife, leave a few next year.