Thaumatopsis pexellus, the woolly grass-veneer, is a moth in the Crambidae family. It was described by Zeller in 1863. It is found in most of North America. The habitat consists of grasslands. The wingspan is 21-32 mm. The forewings are yellowish grey with a whitish line, the outer half bounded above by a thicker dark brown line. There is a terminal row of three to five dark dots. Adults are on wing from July to early September in most of the range. The larvae feed on various grasses.