With leaf-mining insects, identification usually is best achieved from the species of the plant infested and characteristics of the mines. With this leaf miner, the mines will be evident on the leaves of holly plants. Look out for raised areas on holly leaves. Mines are distinctively yellow and white, however, can have areas of brown patching within the blotches. Blotches do tend to cross the central leaf vein.
Holly leaves are unique to other plants which are mined by leaf-mining insects. When larvae leave the leaf, they will make a tear in the mine. Scientists use these tears to identify if larvae left voluntarily, or if they were eaten by something else. We now know that blue tits and parasitic wasps heavily predate these flies.