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Sulfur is an essential element in plants and animals. I measured amounts of sulfur in 4 families of spiders and 22 families of insects collected from created riparian habitat next to the Colorado River in western Arizona. Relation between sulfur mass and body dry-mass, S mu g = 7.2 (body mg), in spiders and insects combined was not allometric. Sulfur concentration, as a mean percentage of body dry-mass, was higher in spiders (1.4%) than in insects (0.65%). Coleoptera contained the lowest sulfur concentration (0.35%) among orders. Sulfur contents also varied among arthropod families but not genera. Similar concentrations of sulfur were measured in insect herbivores (0.64%) and predators (0.73%). Taurine, an amino acid-like compound found in spider venom and silk, likely increased sulfur contents in spiders. Variation in sulfur content among riparian spiders and insects, resulting from concentrations of compounds including taurine, the amino acids methionine and cysteine, and their metabolites, may influence foraging by insectivorous birds.