Black swallow-wort, Vincetoxicum nigrum, is ubiquitous on Fishers Island. The vine’s entangling tendrils and proliferation of leaves create a green mass that can overgrow and smother adjacent plants The sap of this vine is toxic, which is detrimental to monarch butterflies. According to a University of Rhode Island (URI) fact sheet:
Research has found swallow-wort to be harmful to monarch butterfly populations. Because swallow-wort chokes out native milkweed species, monarchs often lay their eggs on swallow-wort plants, itself a member of the milkweed family. Larvae cannot feed on swallow-wort and, subsequently, the caterpillars die which further reduces the already endangered monarch populations.1
There are no simple, conventional methods for controlling black swallow-wort and its related species, pale swallow-wort, V. rossicum. One potential approach is biocontrol: the deployment of an herbivorous species that seeks out and exclusively feeds upon the undesirable plant.
After many years of testing, the University of Rhode Island Biocontrol Laboratory received federal permission in 2017 to release a species of moth, Hypena opulenta, whose larval stage feeds on the swallow-worts. Researchers, who demonstrated that the Hypena larvae consume exclusively swallow-worts and no other species, have been piloting the project with landholders across the northeast.2
HLFM Land Trust Hypena opulenta enclosure. Photo by Jack Schneider.