The Butterbur (Hydraecia petasitis) is a species of moth in the family Noctuidae.

It is found from most of Europe, east to Siberia and Japan.

Forewing dull purplish grey, shaded with olive brown; the median shade, the outer half of median area, the terminal area except at apex, and a costal patch before submarginal line, all of this latter colour; lines as in micacea, but the outer line more curved, sometimes visibly bent on vein 5; submarginal line generally preceded by a narrow dark cloud; the stigmata large, pale grey, with dark outlines; hindwing dull dark grey with a darker outer line and submarginal cloud; continental specimens, = vindelicia Frr., are larger and better marked than the dull British petasitis.

Larva dirty bone-colour, with the dark dorsal vessel showing through; the tubercles black; spiracles white in black rings; head, thoracic, and anal plates brown.

The larvae feed on Petasites hybridus from within the stem and later the roots.