A black swallowwort by any other name is still just as toxic
As an Invasives Intern with USFWS in Rhode Island, I have the unfortunate privilege to find some of the worst invasive plants in the country. I’ve engaged in hand to hand combat with oriental bittersweet vines 50 feet tall and sailed through seas of Japanese knotweed. Given all of this, I believe that one of the most dastardly invasives out there is black swallowwort (Vincetoxicum nigrum).
Known also by its street name, the dog strangling vine, this plant has the potential to harm a multitude of different species from all walks of life. Introduced to the United States as an ornamental from Eastern Europe around 1854, black swallowwort can now be found throughout the northeast. Its large shiny dark-green leaves and its sinister looking dark purple to black flowers make it very easy to spot. It’s true that at first glance this vine might not seem too bad, but just beneath its beautiful exterior lays a deadly siren call to all of our beloved monarch butterflies.
While the roots of black swallowwort are toxic to mammals, the leaves are equally unpalatable for some insects, which include the monarch butterfly. Given the physical similarities and habitat overlap between black swallowwort and the common native monarch host plant, milkweed, adult monarchs will occasionally lay their eggs on the invasive vine. The result is mass mortality of monarch larvae, and yet another blow to our efforts in restoring their population numbers.
Instead of throwing in the towel and continuing to allow black swallowwort to plague our lands, livestock and butterflies, an enterprising team out of the University of Rhode Island is experimenting with different insects and other biocontrol agents. Their goal is to find the right candidate that will stem the tide of the swallowwort invasion. Given more time and the right resources, we may soon have a new weapon with which to strike back against this reckless invader.
Black swallowwort, the dog strangling vine, my worst nightmare; any one of these names could be applied to this robust invasive plant species, but regardless of its label, black swallowwort continues to be a toxic plant that causes untold harm to us and to threatened species that we are trying to protect.