Laothoe populi is a large (wingspan 70–100 mm (2.8–3.9 in)), odd-looking species of moth, due to its habit of resting with its hindwings held further forward than (but still half hidden by) the forewings.

The species lacks a frenulum joining the wings together, and is said to look like a cluster of dead leaves of the main host, poplar.

When disturbed, the moth will suddenly reveal a bright orange-red basal patch on the hindwing, possibly as a distraction or startle display.

The egg is large, spherical, pale green, and glossy, and is laid singly or in pairs on the underside of leaves of the host plant.

Laothoe populi feeds mainly on poplar and aspen, but sometimes on willow, alder, apple, tomato, birch, elm, oak and ash.