Help Stop Black Swallow-Wort in Somerville This Summer

The City of Somerville is partnering with community groups again this year to raise awareness about black swallow-wort (BSW), a very aggressive and invasive, non-native weed that can be found throughout Somerville. BSW displaces native plants and habitats, threatens butterflies and songbirds, and is toxic to deer and livestock. It is especially harmful to the monarch butterfly population because it 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 residents to remove BSW when they see it. The BSW plant has shiny green leaves that come in pairs along winding vines often found around fences and shrubs. It 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 because it will resprout.

To help spread the word, the City is seeking volunteers to distribute informational door hangers about BSW and how to remove it. Door hangers are available for curbside pickup through mid-July at the Somerville Central Library, 79 Highland Avenue.

For more information about BSW, best practices for removing it, and other invasive plants, visit

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