The life cycles of the seed bugs, Kleidocerys punctatus Distant and Kleidocerys virescens F. (Hemiptera: Lygaeidae: Ischnorhynchinae), are reported for the first time. Description of all immature stages and adults are included. Adults and nymphs of K. punctatus are associated with several species of Alnus (Betulaceae), while those of K. virescens are associated with Nicotiana glauca Graham, Nicotiana tabacum L. (Solanaceae), and Buddleia crotonoides A. Gray and Buddleia sp. (Loganiaceae). Adults and nymphs feed mainly on the seeds, inside the dry fruit, but they also take plant juices from other reproductive and vegetative structures. Illustrations of the eggs, all nymphal instars, and the adults, as well as notes on their biology and their distribution in Mexico, are included.