Lasiocampa quercus, the oak eggar,[1] is a common moth of the family Lasiocampidae found in Europe, including Britain and Ireland.

It feeds on a variety of plant species (mainly heather and bilberry), and may develop over two years in higher latitudes, where it may be known as the northern eggar.

Its specific name quercus refers to the fact that its cocoon generally resembles an acorn, not that its primary food source is oak.

The oak eggar's habitat is wide-ranging, including scrub, heath, moor, downland, hedges and sea cliffs, reflecting the larva's very varied range of food plants.

The caterpillar pupates on the ground inside a silken cocoon, the exterior of which is hard and yellowish, and resembles an acorn, hence the moth's name.