Excuse me, what kind of bug is this? How to treat it? Eat all the willow leaves?

The inchworm is the larva of the foot moth.

It belongs to arthropods, Insecta, Lepidoptera, and geometridae. The inchworm has a slender body, bends and stretches like an arch bridge when moving, and can stretch obliquely like a branch when at rest. Totally perverted. Adults have large wings, slender bodies, short hairs and filiform or feathery antennae, which are called "foot moths".