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Somerville Residents: Help Stop Black Swallow-Wort This Summer

Invasive Species Displaces Native Plants and is Toxic to Butterflies and Deer

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.

Why Black Swallow-Wort Is Unwelcome in Somerville

BSW displaces native plants and habitats, threatens butterflies and songbirds, and is toxic to deer. 

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.

How to Spot and Remove Black Swallow-Wort

BSW pods start to appear in Somerville in late May and early June, 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 thin green pods that are important 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 roots should be completely taken up 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 has created door hangers about BSW and how to remove it. Door hangers are available for pickup from May through mid-July at the Somerville City Hall Welcome Desk (93 Highland Avenue). Please pick some up and distribute them in Somerville.

Black Swallow Wort

Individuals with disabilities who need auxiliary aids and services for effective communication, written materials in alternative formats, or reasonable modifications in policies and procedures, in order to access the programs and activities of the City of Somerville or to attend meetings, should contact the City’s ADA Coordinator, Adrienne Pomeroy, at 617-625-6600 x2059 or

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