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There are three European species of swallow-worts found in North America: Vincetoxicum nigrum (L.) Moench (black swallow-wort), Vincetoxicum rossicum (Kleo.) Barb. (pale swallow-wort or dog strangling-vine), and Vincetoxicum hirundinaria Medik. (white swallow-wort) (Sheeley and Raynal, 1996). Swallow-worts are in the family Asclepiadaceae. Vincetoxicum nigrum and V. rossicum now are naturalized in northeastern North America, and both are invasive in natural areas and abandoned pastures (Lawlor, 2000). Swallow-worts are found in gardens and fields, along fencerows, roadways, grassy slopes, wooded edges, and streambanks. Tangled masses of swallow-wort vines shade and suppress native plants (Sheeley and Raynal, 1996). In Rhode Island, heavy growth of V. nigrum reduces the effectiveness of electric fences around pastures (Minto, pers. comm.). Loss of native plant species reduces habitat value for wildlife (Christensen, 1998). Vincetoxicum hirundinaria occurs sparsely in the northeast (Gleason and Cronquist, 1963), and Sheeley and Raynal (1996) suggest that this species is not well established in North America.