(Peyerimhoff, 1863)[Synonyms: inquilina]
Wingspan c. 15mm.
This species is distinctive for its rather long and narrow forewings, with a horseshoe-shaped whitish blotch on the dorsum. The hindwings are whitish with a dark border.
The larvae feed inside oak-apple galls and other, spongy galls made by Hymenoptera on oak (Quercus). Their presence is sometimes betrayed by frass exuded from the gall.
Adult moths fly early in the year, from March to May, and can sometimes be found on the wing in the afternoon. They also fly later at night and come to light.