SeasonalitySpecimens have been collected from mid June through mid July.
IdentificationPhausis rhombica can easily be distinguished from other Alberta fireflies. While some lampyrids may be the same size (6-7mm), no other Alberta genus has the uniform colouration (brown-black) with two large kidney-shaped translucent spots in the anterior portion of the pronotum directly above the eyes. Unlike other Alberta Lampyridae, Phausis species also have a glassy bead, easily visible under a microscope, at the end of the last antennal segment. Currently, no other Phausis species is known to occur in Alberta, though P. nigra has been collected from Fernie, B.C. (Fender 1966), and likely ranges into southwestern Alberta. Phausis rhombica can be distinguished from other Phausis species, including P. nigra, by characteristics of the pronotum. Viewed dorsally, the pronotum is widest at the base and narrows anteriorly, giving it a trapezoidal shape. The two anterior angles may be somewhat obscure, but they keep the pronotum from appearing uniformly rounded. The anterior pronotal margin is feebly arced in most specimens, and in some this arc appears slightly notched in the center. Features of the scutellum are also useful in identifying P. rhombica. The scutellum is subspatulate (roughly pear-shaped), finely notched at the apex, and has a groove running from its center to the notch at the apex. The scutellum also bears small, sparse punctures.