Help Stop the Spread of Black Swallow-Wort in Somerville This Summer

With gardening season in full swing, the City of Somerville is asking community members to help stop the spread of Black Swallow-Wort (BSW). 

What is Black Swallow-Wort?

BSW is a fast-spreading, non-native plant that crowds out native species, disrupts natural habitats, and poses serious risks to butterflies, birds, deer, and even livestock.  Pollinators like monarch butterflies are at great risk because they often mistake BSW for milkweed plants relied on for reproduction. When monarchs lay their eggs on BSW, their larvae hatch and feed on its toxic leaves, only to die shortly after.

BSW appears across Somerville, and we need your help to remove it. 

How to Identify BSW

• Leaves: Shiny, dark green, and arranged in pairs along twining vines—often seen wrapping around fences and shrubs.
• Flowers: Small, dark purple blooms with five petals and a green center, appearing in early summer.
• Pods: Slim, green seed pods begin forming in June. These MUST be removed before they turn brown and release seeds into the wind.

To download photos identifying black swallow-wort click here: Black Swallow Wort Identification

For more information on invasive species of plants impacting Somerville, visit our Plantings in Public Spaces page. 

Help Stop the Spread of BSW:

• Remove It: If you spot BSW, pull up the entire plant by the roots, and dispose in a sealed trash bag. Do not compost or place in yard waste bags.
• Join a Removal Event: Connect with local groups working to preserve local biodiversity:
  • Mystic River Watershed Association (mysticriver.org)
  • Green & Open Somerville (greenopensomerville.org)
• Get the Word Out: Door hangers are available for pickup now through mid-July at the Somerville City Hall welcome desk (93 Highland Ave.). Please pick some up and distribute them in Somerville. 

Want to learn how to do more for local pollinators? Somerville’s Pollinator Action Plan provides simple, effective ways to support bees, butterflies, and other essential species in your yard and neighborhood. 

To review the plan, visit voice.somervillema.gov/somerville-pollinator-action-plan.

Persons with disabilities who need auxiliary aids and services for effective communication (i.e., CART, ASL), written materials in alternative formats, or reasonable modifications in policies and procedures to access the programs, activities, and meetings of the City of Somerville should please contact Adrienne Pomeroy in advance at 617-625-6600 x 2059 or apomeroy@somervillema.gov. 

If you need assistance translating or understanding this information, please call 311 (617-666-3311) or contact us at somerviva@somervillema.gov. The City of Somerville can provide you with an interpreter for free.

This event will be videotaped by the City’s GovTV team. Watch it on-demand with optional closed-captioning (select the CC icon) on YouTube.com/SomervilleCityTV. Or watch on cable TV at GovTV (somervillema.gov/video) Comcast Ch. 22 and GovTV Astound (RCN) Ch. 13 & 613. Videos generally post within one business day of recording.