Brimstone Moth (Opisthograptis luteolata)

Brimstone Moth (Opisthograptis luteolata)

Observation - Brimstone Moth (Opisthograptis luteolata) - UK and Ireland. Description: Caterpillar 16-18mm long on Hawthorn. The small spike in the middle of the back looks distinctive. Can anyone offer an ID, please? Edit: Changed to match nightfly's ID. Many thanks.

Caterpillar 16-18mm long on Hawthorn. The small spike in the middle of the back looks distinctive. Can anyone offer an ID, please?
Edit: Changed to match nightfly's ID. Many thanks.