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A moderate-sized species with a wingspan of 58 - 62mm. Forewings broader than in O. rimosa and O. canadensis, with a width:length ratio of 0.34 - 0.36 (0.29 - 0.31 in canadensis and rimosa) (Simons 1954). Red basal forewing membranes and basal half of costa. Pronotum, mesonotum and abdominal segments shining black with narrow orange borders. Underside with more orange than dorsum, legs orange with black at segment joints. Male valve usually black. Most similar to O. occidentalis, but according to Davis (1919) bella has a slight bluish tint to the black body which is absent in occidentalis. The basal forewing cell is clouded or black rather than clear, and the head is narrower and less blunt compared to occidentalis. Male genitalia of bella and occidentalis similar, with broad, sinuate apical border compared to the defined notch of O. luteobasalis. Last ventral abdominal segment of female with one notch in bella and occidentalis, two in occidentalis.

Adults lay eggs into the twigs of a number of hosts (Simons 1954). The male song consists of a continuous series of clicks running together (Davis 1921). Length of immature stage unknown, but undoubtedly several years as in other species of the genus.

In Alberta, recorded from the Jasper and Waterton region (Strickland 1953). Occurs from British Columbia and Alberta south through most western states (Montana, Idaho, Wyoming, Colorado, Kansas, Utah, Washington, Oregon) to at least New Mexico and California (Davis 1919, Simons 1954).