Profenusa thomsoni, the amber-marked birch leaf miner,[2] is a species of sawfly in the family Tenthredinidae.

It develops inside a leaf blade, the egg usually being laid close to the midrib and the larva hollowing out a "blotch"-shaped cavity.

The larvae feed on the mesophyll tissue inside the leaf, creating a pale brownish "blotch"-shaped mine.

When fully mature, the larvae emerge through the underside of the leaf and fall to the ground, where they make chambers in which to pupate.

[5] P. thomsoni is uncommon in Europe, but after its introduction into North America, populations built up rapidly.