The
wingspan is 13–18 mm. Adults are on wing from July to August and again from September to May of the following year after hibernation. The larvae feed on rosebay willowherb (
Chamaenerion angustifolium). The larvae feed inside the stem of their host plant, usually in the flowering part. Feeding causes a
gall to be formed. Larvae of the second generation usually live in a seedpod. Larvae of the first generation are found from May to June and larvae of the second generation are found from July to August. ==References==