[2][3][4] It has a flexible univoltine or semivoltine (one- or two-year) lifecycle, depending on the timing of its hatching, and is unusual in being able to spend two winters as diapause nymphs before reaching maturity.

Adults measure 25–35 millimetres (2+1⁄2–3+1⁄2 cm) in length, and have a shiny, uniformly black to blackish-brown body, with brown tarsi and maxillary and labial palps.

[8] Overwintering nymphs were able to survive laboratory supercooling experiments in the −5 to −8 °C (23 to 18 °F) temperature range, enduring 12 hours of tissue freezing,[7] as well as recover from burial in ice.

[1] Primarily an outdoors species, populations are adaptable to living indoors in houses and buildings where food is stored, prepared, or served.

[5][9] A P. japonica nymph alone or in sparse populations accumulates a viscous secretion along its rear dorsal surface, droplets of which it can be splashed some distance toward a threat through a shaking action.