by Mary Holbrow. Monarch butterflies are threatened by the invasive black swallow-wort, a deadly host plant for their larvae. The plant is spreading throughout New England and crowding out native plants. The star-shaped black swallow-wort flowers, below left, are tiny and purple. The Monarch above had a better choice in the butterfly garden at the Museum of Science.
On July 21 volunteers Helen Snively and Rebecca Ramsay of the Friends of Fresh Pond Reservation (FFPR) stacked a table in the lobby of the Cambridge Main Library with black swallow-wort vines and seed pods, informational brochures, and Pod Patrol lapel buttons promoting joint efforts by FFPR and City of Cambridge to limit the spread of black swallow-wort. Snively and Ramsay were there to talk with Saturday morning library-goers about ways to help control the noxious weed.
“You’ve seen this plant," Snively said. "It’s everywhere. I pulled this piece off a chainlink fence on Cambridge Street. It’s a member of the milkweed family, which is the Monarch babies' normal food.”
The female butterflies mistake the swallow-wort for native milkweed and lay their eggs on it, she explained. The plant is toxic to the caterpillars. Snively and Ramsay urged residents to collect the pods and destroy them, and to pull or dig the plants if possible.
The swallow-wort competes for space and nutrients with the milkweed and other native flora. It has expanded throughout New England to the point where the National Park Service has rated it “Least Wanted.” Its scientific name, Cynanchum, means "dog-strangler" according to David Gledhill's book, The Names of Plants, Cambridge University Press (2002).
“And it’s absolutely lethal if you get it growing in your garden,” Snively said. She described the spread of black swallow-wort in the Sacramento Street community garden.
“You put in a tomato seedling, and a week later you come in and this thing is wrapped around it. Good-bye tomato plant.”
This isn't the first time FFPR has come to the library to spread the word about the black swallow-wort, Rebecca Ramsay said. Earlier the organization teamed up with the city to form Pod Patrols -- volunteer organizations that have collected the seed pods in the city and at Fresh Pond. The groups help to educate the public about environmental issues and the importance of biological diversity.