Lunar Hornet Moth Sesia bembeciformis
Wingspan 32-42 mm.
One of several similar 'mimic' species, known as Clearwings, this is one of the largest, and presents a fearsome sight to the uninitiated.
Best looked for in July, as the adults emerge and rest low down on the trunks of the foodplants, sallow and willow (Salix spp.).
The eggs are laid on the bark, and the larvae burrow into the wood, feeding internally.