A survey of arthropods visiting flowers of California pipevine, Aristolochia californica Torr. (Aristolochiaceae), was conducted during 2017 and 2018. Collecting produced 1725 individuals in 75 terminal taxa. Over the two years, a residential backyard produced more terminal taxa (70) and individuals (1539) than flowers in an upland grassland (27 terminal taxa, 186 individuals). Diptera: Mycetophilidae were the dominate arthropod group attracted to the flowers, accounting for 77.8% of visitors and represented by 17 genera and 28 morphospecies, with Mycetophila Meigen, 1803 being most diverse with 12 morphospecies. The superfamily Sciaroidea (Keroplatidae, Mycetophilidae, Sciaridae) had 33 morphospecies and 1505 specimens representing 87.2% of the total arthropods. The arthropods could be grouped into the following guilds: potential pollinators, fluid feeders, predators, parasites, scavengers and temporary residents.