The larval mining in the leaf tissues produces conspicuous blotches or blisters on the leaves which later turn brown. Heavily infested birches may be almost completely browned and appear to have been scorched by fire. The tops of the trees are often the most seriously affected portions. There are one to two generations per year in Vermont depending upon location and seasonal temperatures. The first generation causes the most damage.
Adults begin egg laying in the spring and the leaves unfold.
All soft leaf tissues are favorable for larval development. The second generation may also attack succulent sprout growth. The adult sawflies do not oviposit on older foliage. A healthy tree can normally lose nearly all of its leaves without being seriously injured. Yellow and black birch are not known to be attacked.