Phytophagous insects representing six orders, 14 families, and 18 identified and 3 unidentified species are reported as comprising the insect fauna of spiny c1otbur, Xanthium spinosum L. (Compositae), in southern California. Similarly, insects representing six orders, 29 families, and 60 species are reported as associates of cocklebur, X. strumarium L. Most insects attacking these introduced weeds were polyphagous, sap or foliage-feeding species. Many also were ragweed, Ambrosia spp., insects. One-third of the insect species collected from spiny clotbur and 15% of the cocklebur insects were endophagous as immatures. Eighty-three percent and 75% of the 18 and 52 associates identified to species are newly reported from spiny clotbur and cocklebur, respectively. Sixty-one percent and 44% of the identified associates of these two weeds, respectively, were major or minor pests of cultivars. Also. five (24%) and eight (13%) of these identified associates, respectively, were stenophagous species, their hosts apparently confined to the tribe Heliantheae