Thaumatopsis pexellus, the woolly grass-veneer, is a moth in the family Crambidae. It was described by Philipp Christoph Zeller in 1863. It is found in most of North America. The habitat consists of grasslands.
The wingspan is 21âÂÂ32 mm. Adults are on wing from July to early September in most of the range.
The larvae feed on various grasses.