Gastropacha quercifolia, the lappet, is a moth of the family Lasiocampidae.

Meyrick describes it thus - forewings with 9 to termen; red-brown, with purple-bluish gloss, towards costa blackish-mixed, dorsally ferruginous; first, second, and praesubterminal lines blackish-grey, waved, bent near costa; a blackish-grey discal mark; termen waved-dentate.

Hindwings as forewings, but lines indistinct, straight, costal area ferruginous, with about six blackish pseudoneuria; 8 connected with cell by long bar.

Larva dark grey or brown; whitish dorsal marks on 3 and 4; 2nd and 3rd incisions deep indigo-blue; a prominence on 1 2; a subspiracular series of tubercles and fringe of pale hairs.

[1] The larvae feed on Crataegus, Prunus spinosa, willow and oak.