Monarch Butterflies - An Invasive Plant Threat to Monarch Caterpillars

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Caution: The two species of Cynanchum below are invasive species. Monarchs will lay eggs on them, but the caterpillars will die:

As black swallow-wort, Vincetoxicum nigrum L. Moench, and pale swallow-wort, V. rossicum (Kleopow) Barbar., spread throughout the northeastern United States and southern Canada, there is concern about the impact of these invasive plants on populations of the native North American monarch butterfly Danaus plexippus L.

In none of our laboratory or field evaluations was there any survival of monarch larvae on Vincetoxicum species.

BioOne Online Journals - Monarch Butterfly Oviposition on Swallow-Worts (Vincetoxicum spp.)

If you use Cynanchum species for host plants, be sure that you do not use these two species. If these two species are present in your area, please try to eradicate them. They could become a serious threat to monarch populations.

Cynanchum louiseae (syn. Vincetoxicum nigrum) – Louise's swallow-wort
Black dog-strangling vine, black swallowwort: Cynanchum louiseae (Gentianales: Asclepiadaceae): Invasive Plant Atlas of the United States

Cynanchum rossicum (syn. Vincetoxicum rossicum) – European/pale swallow-wort
dog-strangling vine, European swallowwort: Cynanchum rossicum (Gentianales: Asclepiadaceae): Invasive Plant Atlas of the United States

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