Introduced European weevil now threatens over 30 native North American thistles

In 1969, U.S. wildlife and agricultural agencies released the European weevil Rhinocyllus conicus to attack the invasive musk thistle (Carduus nutans) that was damaging pasture lands. Subsequent surveys revealed the insect establishing itself on more than 30 native thistle species, with larvae consuming developing seeds inside flower heads and cutting seed production by up to 80 percent. Research archived by the University of Maryland shows that rare plants such as Pitcher's thistle, Platt's thistle, and Ownbey's thistle have suffered significant reproductive losses.

The weevil spread beyond farms into national parks, the Great Plains, Rocky Mountains, and wetland habitats in California. Although the USDA’s Animal and Plant Health Inspection Service revoked permits and stopped new releases, the beetle remains entrenched in the wild, continuing to threaten native thistle populations.