Stygia australis is a species of moth of the family Cossidae.

The abdomen is elongated, blue-black in colour with a small anal tuft.

The fore-wings are narrow, brownish in the male, with greyish-white markings, and the hind-wings are rounded, blue-black, with a large white spot in the centre.

In the female the fore-wings are reddish-yellow, varied with brownish, and the hind-wings are coloured as in the male.

The larva, which is smooth and whitish, with the head and thoracic segments yellowish, lives in the roots and stalks of Echium italicum".