We compared the insect and arachnid species found in spring and summer samples of necrotic tissue of three species of columnar cacti, cardón [Pachycereus pringlei (S. Watson) Britten and Rose], organ-pipe (Stenocereus thurberi Buxb.), and senita [Lophocereus schottii (Engelm.) Britten and Rose] (all Cactaceae), endemic to the Sonoran Desert of North America. A total of 9380 arthropods belonging to 34 species, 23 families, 10 orders, and 2 classes were collected in 36 samples. Arthropod communities differed in composition among host cacti, as well as between seasons. These differences may be a function of variation in host characteristics, such as chemical composition and abiotic factors, such as water content or temperature.