Right about now you will be seeing the pods of black swallow-wort forming all over Somerville.
There’s more information about the negative impact this plant has on native ecosystems in this Wikipedia article: http://en.wikipedia.org/wiki/Cynanchum_louiseae
One thing it is guilty of is reducing the monarch butterfly population. It crowds out other milkweed species, on which the monarch butterfly lays its eggs. When the monarch lays its eggs on black swallow-wort, the larvae do not survive to adulthood (paraphrasing from the above article).
Do your part to combat this loathsome invasive vine. Pick off the pods in order to stop the seeds from spreading. Don’t compost them; throw them out with the trash. If you find the vine in your own yard, you have several options, as outlined in this Wikipedia article. Digging it out is best, but for places where that’s difficult, you can at least cut it down in order to prevent seed pods from forming.