1. Either the axil of the scale is galled, or the galled fruit is distinctly coalescent with the scale; window-pit absent..........skuhravae sp. n.
— Galling of the fruit, the gall is in ripe situation never coalescent with the scale..........2
2. Window-pit absent or indistinct, gall subrotund and glabrous, wings of fruit often completely reduced..........tarda sp. n.
— Window-pit(s) distinct..........[all other Semudobia spp.]
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Gall...galling of the fruit; the fruit is button-like swollen, subrotund, wings are completely or nearly completely reduced; window-pit rather indistinct (B. pubescens).
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[Record from B. papyrifera was from a cultivated tree in Quebec where "an introduction of infected fruits of Palaearctic birch species is supposed". Only otherwise recorded from North America on introduced B. pendula in Montana.]

Betula (birch)
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Swollen bract or ovary of female catkin...Semudobia spp.

Five species of Semudobia are known from North America, three native and two originally introduced from Europe in seeds of Betula pendula. One of the three native species is Holoarctic, the two others are Nearctic only. The biology of all five species is generally similar. Eggs are deposited in spring between the bracts and flowers. Usually only one larva infests a bract or ovary. Pupation occurs in the gall the following spring.
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S. tarda Roskam, an immigrant from Europe. Host: B. pendula.