Caloptilia robustella (commonly known as new oak slender)[1] is a moth of the family Gracillariidae. It is known from all of Europe, except the Balkan Peninsula.
The wingspan is 10-. There are multiple generations per year, with adults on wing between April and November.[2]
The larvae feed on Fagus sylvatica and Quercus robur. They mine the leaves of their host plant. The mine starts as a narrow lower-surface epidermal gallery, regularly intersecting itself. Later, the mine becomes full depth. It remains a small mine, either rectangular or (more frequently) a triangle in a vein axle, with frass along the sides. Older larvae leave the mine and continue feeding in a leaf roll. Pupation takes place in a white cocoon.[3]