Photo © Gail Hampshire
Plusia festucae (gold spot) is a species of moth of the family Noctuidae. It is found throughout the Palearctic realm from Ireland to Japan.
The wingspan is 34-46 mm. Forewing deep golden brown, with a golden metallic sheen at base of costa, on inner margin of median area, and on an oblique patch before apex; lines all oblique, dark brown; veins dark brown; at base of vein 2 a large silvery rounded blotch, with a smaller, more elongate, one beyond it; the lowest streak of the apical blotch, below vein 6, and a spot at base of costa are also silvery; hindwing bronzy fuscous, with pinkish fringe.
The moth flies from June to September depending on the location.
Larva green; dorsal line dark green, edged with white; subdorsal and lateral lines white; spiracular yellowish; head green. The larvae feed on Carex, Sparganium erectum, Iris pseudacorus and Alisma. Pupates in a whitish cocoon on the underside of a blade of grass, doubled over for the purpose.
Source: Wikipedia
The primary larval foodplants are Branched Bur-reed (Sparganium erectum), Glaucous Sedge (Carex flacca), grasses, rushes (Juncus spp.), Tufted-sedge (Carex elata), Water-plantain (Alisma plantago-aquatica), Wood Small-reed (Calamagrostis epigejos), Yellow Iris (Iris pseudacorus) and Yorkshire-fog (Holcus lanatus).