Tamarix ramosissima Ledebour (Tamaricaceae) is an invasive shrubby tree naturalized in riparian areas throughout the western United States. Biomasses of arthropod taxa on T. ramosissima branches were quantified as dry mass per plant dry mass on three trees at each of three sites near surface water at Las Vegas Wash, NV, during 2002 and 2003. Biomass of two phytophagous-arthropod taxa, Opsius stactogalus Fieber (Homoptera: Cicadellidae) and Chionaspis spp. (Homoptera: Diaspididae), comprised 97.7% of arthropod biomass and varied among sites and among trees within sites. Their biomass was positively related to percent water of branches. Biomass of O. stactogalus was strongly associated with those of its parasites, Polynema saga (Girault) (Hymenoptera: Mymaridae) and Gonatopus sp. (Hymenoptera: Dryinidae), and predatory Dictynidae (Araneae) and weakly associated with those of omnivorous Attalus spp. (Coleoptera: Melyridae) and Formica xerophila M. Smith (Hymenoptera: Formicidae). Biomass of Chionaspis spp. was only associated with biomass of predatory Cybocephalus californicus Horn (Coleoptera: Nitidulidae). Biomass of predatory Salticidae (Araneae) was not associated with that of either phytophagous arthropod taxon. Low percentage of secondary-consumer biomass and large fluctuations in biomasses of O. stactogalus and Chionaspis spp. between years suggest populations of phytophagous arthropods on T. ramosissima are not regulated by natural enemies. T. ramosissima branches offer vertebrates arthropod prey with low diversity and highly variable biomass.