Help Stop Black Swallow-Wort in Somerville

The City of Somerville is partnering with community groups to raise awareness about black swallow-wort (BSW), a very aggressive and invasive, non-native weed that can be found throughout Somerville. It displaces native plants and habitats, threatens butterflies and songbirds, and is toxic to deer and livestock. BSW is especially harmful to the monarch butterfly population as BSW resembles milkweed, where monarchs lay their eggs, and once the monarch larvae hatch they die from eating the toxic BSW leaves.

BSW pods have already started to appear in Somerville this season, and the City and community groups are asking community members to remove BSW when they see it. Volunteers are also being sought to help distribute informational door hangers in their neighborhoods about BSW, how to identify it, how to and remove it. 

The BSW plant has shiny, green leaves that come in pairs along winding vines that are often found around fences and shrubs. It also has slim, green pods that appear in June, which are imperative to remove before they turn brown and disperse wind-borne seeds. BSW also has small, dark purple flowers that grow in clusters with five petals and a green center. Whenever possible BSW should be uprooted completely and the pods should be removed. To dispose of the plant, be sure to place all of it in a sealed trash bag. Do not compost or place BSW in paper or yard waste bags, they will resprout.

To pick up door hangers now through mid-July, please visit the Somerville Central Library at 79 Highland for contactless pickup. Because there is a limited quantity, we ask that each person take a maximum of  20 door hangers.

Thank you for helping eradicate this invasive species!