Polymixis argillaceago is a moth of the Noctuidae family. It is found in south-western Europe and the Maghreb countries. The wingspan is 34–39 mm. Adults are on wing from September to October in one generation per year. The larvae feed on various herbaceous plants. Young larvae are green with a conspicuous whitish stripe at the side. After the fifth instar, they turn brown. The species overwinters in the larval stage.