The adult flies are 2mm long and greyish brown in colour. They feed by rasping the leaf surface, leaving small pale spots on the upper leaf surface.
More significant markings are caused by the creamy white larvae. They eat the internal tissues of the leaves and cause whitish brown discoloured blotches. The mines typically have a pale edge around the darker brownish centre.
There are two generations during the summer and by August each leaf can be affected by several mines.