A rough, hairless, light-green to pink-red gall on the lamina of Populus tremuloides, protroding on both sides, with a globular mass below and a puckered pair of protruding lips on either side of a slit-like opening above. It varies from nearly globular to flattened against the leaf. Either single or in scattered groups. Observed from Alaska to Quebec and south to Colorado between May and September.

This gall resembles that of Harmandiola cavernosa known in Europe from Populus alba and tremula.

This gall morphotype can be distinguished from other midge galls on Populus leaves by the following traits:

• Larva concealed within galled tissue, protruding primarily on the lower side of the leaf
• Noticeably protruding lips on the upper side of the leaf surrounding a linear slit exit hole