About Perizoma affinitata (Stephens, 1831)
Perizoma affinitata, commonly known as the rivulet, is a moth species belonging to the family Geometridae. It was first described by James Francis Stephens in 1831, and is found across most of Europe. This species has a wingspan of 24–30 mm. It is characterized by a narrow white postmedian band on the forewing, and particularly by a dark hindwing that only bears a narrow, divided white or whitish band. According to Otto Staudinger, it is distributed across central and northern Europe and Romania, with records from northern and western Germany, and less commonly from England. The form rivinata Fisch.-Rossl. has much extended white colouring on the forewing, and a hindwing that is broadly or almost entirely white. This form occurs mainly in northern or mountain districts, but sometimes appears as an aberration alongside the typical form in England, northern Norway, the Alps, and the Carpathians. The form magistraria Trti. and Verity is larger than the typical species. Its forewing is grey rather than brown, darker than that of hydrata, and has a broader white band; its hindwing is greyish with a double whitish band, and its underside matches that of rivinata. This form is found at Terme di Valdieri in the Maritime Alps. The larva of Perizoma affinitata is moderately robust, pale pink, with a dark head capsule and dark colouring on the dorsal side of its first body segment. Adult moths inhabit forest edges, hedges, and flower meadows. The larvae feed on plants in the Silene genus, including Silene dioica. Larvae can be found from June to September, and the species overwinters in its pupal stage.
