Phytophagous insects ofCarduus nutansL. (Compositae) in South Dakota are reported. Ninety-eight species are noted, including 3 which have endophagous habits; i.e.,Papaipema nebrisGuenée (Lepidoptera: Noctuidae),Platyptila carduidactlysRiley (Lepidoptera: Pterophoridae) andHomoeosoma ellectellumHulst (Lepidoptera: Pyralidae). Nearly half of the species were collected only once in the samples and are therefore considered rare or transient. Comparisons with European thistle insects indicate musk thistle in South Dakota has not been thoroughly exploited by native insects.