The bow-legged bug genus Hyalymenus Amyot & Serville, 1843 (Hemiptera: Heteroptera: Coreoidea: Alydidae) includes 20 New World species. Of these, nymphs of only one species, H. tarsatus (Fabricius, 1803), have been described, and the description was restricted to the fifth instar. Nine specimens of H. subinermis Van Duzee, 1923, representing the first through the fifth instars, were collected on two Schinus terebinthifolia Raddi (Anacardiaceae) shrubs from a residential neighborhood (approximately 177,828 m² surveyed) in Long Beach, California, U.S.A. in June 2021. Several other locations within the city were surveyed (i.e., parks, residential areas, and riparian habitats; approximately 109,177 m² surveyed, collectively), but this species was not observed on other S. terebinthifolia plants or other plant species in these areas. Here, we give the first California record for H. subinermis, describe the five nymphal instars, provide habitus images of each instar, and discuss the distribution of the species in California, known host plants, and putative ant models that nymphs may mimic.