Narnia femorata Stål (Hemiptera: Heteroptera: Coreidae) is a leaffooted bug commonly found on Opuntia and Ferocactus cacti (Cactaceae) in southern New Mexico. Although general information has been published on the biology of this species, detailed studies are limited, particularly in America north of Mexico. Therefore, we conducted a study of this bug's life history in southern New Mexico from August 2010 to May 2012, reared the bug in the laboratory, and described the immature stages. Six prickly pear cactus plants, Opuntia phaeacantha Engelmann, and four barrel cactus plants, Ferocactus wislizeni (Engelmann) Britton & Rose, were examined weekly to record numbers of the various life stages, adult sex ratios, and behavioral activities. Adults of this apparently bivoltine species overwintered in plant debris at the bases of their host plants. They emerged in late February to deposit eggs in rows along the underside of cactus spines. Nymphs were found from late February through late December. Nymphs of the first generation were most abundant April through June on and around developing flowers of O. phaeacantha. Those of the second generation were most abundant during August and September on maturing fruit of O. phaeacantha and developing flowers and maturing fruit of F. wislizeni. The bug also was reared from egg to adult under controlled laboratory conditions on fruit and pads of O. phaeacantha at 25 ± 0.01 °C under a photoperiod of 14:10 (L:D) h. The incubation period averaged 12.70 d. The five stadia averaged 3.84, 11.00, 12.12, 17.06, and 22.94 d, respectively. Instars can be distinguished readily by differences in several morphological features in addition to body size and coloration.