Thaumatopsis fernaldella is a moth in the Crambidae family. It was described by Kearfott in 1905. It is found in North America, where it has been recorded from Alberta, California, Florida, Maryland, Mississippi, Nevada, New Mexico, Oklahoma, Saskatchewan and Texas. The habitat consists of prairies. The wingspan is 23–31 mm. The forewings are ashy grey to whitish brown with a white median streak and a terminal row of seven dark dots. Adults are on wing from April to October.