This particular plant does not, as its name suggests, affect or harm dogs. Unfortunately, what it does threaten are native plants and ecosystems.
The dog strangling vine, or European swallow-wort, is native to Eastern Europe and has now settled in Canada, particularly in many areas of Southern Ontario. This invasive species has managed to spread like wildfire very successfully and at an alarming rate, mainly through wind dispersal of its feathery seeds. They are easily identified through their leaves, that hold a strong resemblance to their relatives, milkweed leaves, but are smaller and darker. Their pinkish flowers bloom in late May to late July. This vine grows until it can’t support its own weight, whereby growing along the ground and twining into other plants or vegetation.
It is successful at being so invasive as it can grow in a wide range of habitats, from forests to open grasslands and outcompeting native species, especially those that are rare or sensitive. Species that are threatened by the dog strangling vine include alvars and the monarch butterfly, which is currently an at-risk species in Canada.
Research has showed that the vine is not a viable host of monarch butterflies and is likely to pose little direct threat to their populations as oviposition sinks. Another study by Matilla and Otis (2003) showed that when given a choice between hosts over 24 h, 92% of larvae moved to milkweed leaves and consumed 3.94 cm2 of milkweed leaves compared to 2% of larvae that moved to dog-strangler vine and consumed negligible amounts of leaf material (0.01 cm2). Thus, the actual presence of dog strangling vines does not affect the monarch butterfly population. The ability of these highly aggressive plants, however, to out-compete and displace the native host of monarchs, A. syriaca, may pose a more serious threat.
The Nature Conservancy of Canada (NCC) and the Couchiching Conservancy are actively monitoring dog-strangling vine invasions on the Carden Alvar, and an eradication plan is underway. Volunteers help remove these vines over summer seasons, apply spot pesticides and remove seed pods.