The mine starts as a long, slender, slightly tortuous, gradually widening gallery.

The first part being on the under-surface of the leaf, close against the cuticle, showing up white and silvery by reflected light.

It usually follows the midrib or margin of the leaf along its greater extent, sometimes being deflected by the coarser veins.

The colour of the mine is conspicuously white or light green, sometimes discoloured a bright reddish-brown, but patchy in character.

That part of the leaf covering the blotch is, in fleshy leaves, more or less mottled in shades of green according to the closeness of the mine to the outer cuticle.