What you need to know about the dog-strangling vine. Includes habitat, identifying features and what you can do to reduce its impact.
On this page Skip this page navigation
The name “dog-strangling vine” refers to two invasive plants native to Eurasia – black swallowwort and pale swallowwort. These look-alike members of the milkweed family were introduced to the northeastern United States in the mid-1800s for use in gardens. In recent years these perennial vines have spread rapidly throughout central and southern Ontario.
Dog-strangling vine produces bean-shaped seed pods that are four to seven centimetres long. Photo: Greg Bales, NDMNRF
Dog-strangling vine prefers open sunny areas, but can grow well in light shade. It grows aggressively up to two metres high by wrapping itself around trees and other plants, or trailing along the ground. Dense patches of the vine can “strangle” plants and small trees.
The plant can produce up to 2,400 seeds per square metre. The seeds are easily spread by the wind, and new plants can grow from root fragments, making it difficult to destroy. The vine has invaded ravines, hillsides, fence lines, stream banks, roadsides and utility corridors. Dog-strangling vine is also found in prairies, alvars (limestone plains), plantations of pine trees and natural forests.
Dog-strangling vine was first found in Ontario in the late 1800s. Outside its native range, dog-strangling vine is now found in parts of Ontario, southern Quebec and several American states.
Impacts of dog-strangling vine
- Dog-strangling vine forms dense stands that overwhelm and crowd out native plants and young trees, preventing forest regeneration.
- Colonies form mats of interwoven vines that are difficult to walk through and interfere with forest management and recreational activities.
- Leaves and roots may be toxic to livestock. Deer and other browsing animals also avoid dog-strangling vine, which can increase grazing pressure on more palatable native plants.
- The vine threatens the monarch butterfly, a species at risk in Ontario. The butterflies lay their eggs on the plant, but the larvae are unable to complete their life cycle and do not survive.
Dog-strangling vine invading the understory of a woodland. Photo: Greg Bales, NDMNRF
Flowers are pink to dark purple and star-shaped. Photo: Ken Towle
How to identify dog-strangling vine
- Grows one to two metres high by twining onto plants, trees or other structures.
- Leaves are oval with a pointed tip, seven to 12 centimetres long, and grow on opposite sides of the stem.
- Pink to dark purple star-shaped flowers have five petals about five to nine millimetres long.
- The plant produces bean-shaped seed pods four to seven centimetres long that open to release feathery white seeds in late summer.
What you can do
- Learn how to identify dog-strangling vine and other invasive plants, and how to effectively manage these species on your property. See Landowner’s Guide to Controlling Invasive Woodland Plants and Stop the spread of invasive species.
- Avoid using invasive plants in gardens and landscaping.
- Buy native or non-invasive plants from reputable garden suppliers. Native plants provide habitat and food sources for native wildlife. See Grow Me Instead: Beautiful Non-Invasive Plants for Your Garden.
- Dispose of invasive plants in the garbage. Do not put them in the compost or discard them in natural areas. Discarded flowers may produce seeds.
- When hiking, prevent the spread of invasive plants by staying on trails and keeping pets on a leash.
- If you’ve seen dog-strangling vine or other invasive species in the wild, please contact the Invading Species Hotline at
1-800-563-7711, or visit Ontario's invading species awareness program to report a sighting.
- Invasive species centre
- Invasive species in Ontario
- Ontario invasive plants council
- Ontario's invading species awareness program
For more information:
Please contact the Invading Species Hotline at
Bean-shaped seed pods open in late summer, releasing feathery white seeds. Photo: Greg Bales, NDMNRF
This fact sheet may be reproduced for non-commercial purposes.
Cette publication est également disponible en français.
Plants are capable of twining together and growing up to two metres high. Photo: Andrea Hicks, OFAH