Black swallow-wort is an invasive plant species that can interfere with monarch butterfly reproduction. Monarch butterflies help pollinate other plants, so a healthy population is important. If you have black swallow-wort in your yard, now is a good time to get rid of it before its seeds drop. Somerville Urban Ag and Mass Audubon have more information about black swallow-wort and information on how you can get rid of this pesky plant.