The life history of the stink bug Mecidea minor Ruckes (Hemiptera: Heteroptera: Pentatomidae) was studied in the southern half of New Mexico from January 2005 to December 2007, and the egg and nymphal instars are described. This species was active year-round, occurring on various species of grasses but primarily on Lehmann lovegrass, Eragrostis lehmanniana Nees; grama grasses (Bouteloua spp.); Bermuda grass, Cynodon dactylon (L.); and tobosagrass, Pleuraphis mutica Buckley. Adults and late instars (fourth and fifth) were present during winter. The appearance and abundance of the eggs, nymphs, and adults during the year suggest this species is bivoltine with the possibility of a partial third generation. Instars can be distinguished by differences in morphological features, including body size and presence and relative development of wing pads.