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.......... [all other Semudobia spp.]
...
Gall ...galling of the "bract"; the ovoid gall is situated between the spindle of the catkin and the scale; window-pit absent (B. pubescens). In Japanese (Honshu, Azegate, B. ermanii) and American (South Dakota, Black Hills, B. occidentalis) material S. skuhravae is found in fruit galls. These galls have no window-pit and are coalescent with the scale. When gall and scale are separated, the membraneous cocoon of the larva becomes visible.

Betula (birch)
...
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.
...
S. skuhravae Roskam, a Holarctic species. Hosts: B. alleghaniensis, B. occidentalis, B. papyrifera, B. pendula, B. populifolia.