[1][2][3][4][5][6] In Illinois, adults have been observed emerging from overwintering sites in late April, and continue to be observed until early November, and appear to be bivoltine in this area.

[6] Adults are bronze in color, with a white-yellow border around the scutellum,[1] and are 5.0–7.2 millimetres (0.20–0.28 in) in length.

[7] In laboratory conditions, at approximately 24 °C (75 °F), development from eggs to adults has been documented to take between 39 and 50 days, and appears to be affected by the species of host plant.

[6] Mormidea lugens has been documented to feed on timothy, sedges (including Carex shortiana, C. amphibola, C. normalis), as well as deer-tongue grass (Panicum clandestinum), and Bosc's panic-grass (P. boscii).

It has been collected from pale sedge (C. blanda) and wide-leaved spiderwort (Tradescantia subaspera) but has not observed feeding on these species, and deer-tongue grass appears to be an insufficient food source for development.