Leistarcha thaumastica is a moth in the Xyloryctidae family. It was described by Turner in 1946. It is found in Australia, where it has been recorded from New South Wales. The wingspan is about 38 mm. The forewings are grey-whitish lightly sprinkled with fuscous and with a slender median fuscous line from two-fifths nearly to the termen with a short parallel line on its costal side. There are three short streaks running to the costa, one to the apex, several to the termen, and one to the tornus. The hindwings are ochreous-yellow with a pale fuscous suffusion around the apex, termen and tornus.