The life history of the stink bug Mecidea major Sailer was studied in the southern half of New Mexico primarily from January 2005 through December 2007, and the nymphal instars were described.  This species was active throughout the year as adults and nymphs, including the winter months.  It occurred on various species of grasses during this time but primarily on Lehmann lovegrass, Eragrotis lehmanniana Nees; grama grasses, Bouteloua spp.; and tobosagrass, Pleuraphis mutica Buckley.  The times of occurrence and abundance of the eggs, nymphs, and adults suggest this species is bivoltine with the possibility of a third generation.  Instars can be distinguished by several morphological features including body size and presence and relative development of wing pads.