fleck mine

Full depth blotch, not containing frass, and invariably with one, more or less central, usually circular, hole. Made by a larva (usually a Coleophora that operates from the outside. The larva first bites the hole in the epidermis, then from that point it eats away as much leaf tissue as it can reach without fully entering the mine.

Coleophora serratella mine

Coleophora serratella: a typical fleck mine, mined out via the opening, no possibility that frass could be left in the mine.