Pachycnemia hippocastanaria, the horse chestnut moth, is a moth of the family Geometridae. It is found in most of Europe.
The wingspan is 28–32 mm. Adults are on wing from April to May, and again in a partial second generation in August, usually with fewer and smaller moths.
A distinctly southern species in Britain, occurring only on the heaths of the southernmost counties, although in places can be fairly common.
The moths fly in April and May, with a second brood in August, usually with fewer and smaller moths, although in some parts of the country, the autumn brood now appears to produce more records.
Both the English and Latin names refer to the horse chestnut, but the origins of these are unknown, as the larval foodplant is heather (Calluna).
