[1] Ypresiosirex was described from a specimen which was recovered from outcrops of the early Eocene, Ypresian McAbee Fossil Beds near Cache Creek, British Columbia.

The unnamed formation outcropping at the McAbee Fossil Beds preserve an upland temperate flora that was first interpreted as being Microthermal,[2] although further study has shown them to be more mesothermal in nature.

[3] The plant community preserved in the McAbee Fossil Beds site is mostly broadleaf pollen with alder and elm dominating, and may represent a successional forest involving multiple volcanic ash eruptions.

[1] The specific epithet orthosemos is derived from Greek meaning "with vertical stipes", alluding to the corrugated texture of the wing membrane at its base.

[1] Ypresiosirex orthosemos was one of three sawfly species described in Archibald & Rasnitsyn's 2015 paper, the other two being Ulteramus republicensis and Cuspilongus cachecreekensis, from the Klondike Mountain Formation and the McAbee fossil beds respectively.