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A medium-size (3.3.2 cm wingspan) robust "hairy" grey moth. The forewings are steely blue grey except for the costa, which is broadly pale gray-white. The smooth dark grey of the lower half of the forewing extends in an indistinct narrowing stripe to the apex. The subterminal line consists of a series of poorly defined short black streaks or elongated spots, increasing in size toward the lower margin, and lightly marked by white scales along the distal side. The post-median and in particular the antemedian line are each indicated at the costa by a short jagged black line. The hindwings are dark brownish grey. The antennae are simple or nearly so. The related P. cinerea is paler grey and flies in the fall. Pleromelloida conserta has the forewings crossed by one or more complete lines. The genitalia of bonuscula (male genitalia illustrated) and conserta are also very different.

Poorly known; apparently single-brooded. Adults are nocturnal and come to light. The single Alberta specimen was collected on June 30, 2002. In adjacent BC they fly in early spring (late March – May). The host plant(s) of P. bonuscula appear to be unknown. The hosts of the closely related P. cinerea and P. conserta are reported to be snowberry (Symphoricarpos sp.).

The illustrated specimen was collected in open Ponderosa pine grassland at Merritt BC at the end of March, flying with Cucullia pulla (Grt.) and C. strigata (Sm.). I have also collected it in similar habitat at Fairmont, BC in late April. The unusual location and late date of the single Alberta specimen raises the possibility of it being a mislabeled specimen.