This paper reports on the biology of Lithurgopsis apicalis (Cresson) that were found excavating nests in the dead and dying flower/seed stalks of Agave in southern Arizona. Females normally gain entry to the soft inner tissue of the stalk by seeking out naturally occurring longitudinal cracks in the hard outer surface of the stalk. Once inside they chew branching tunnels through the soft plant tissue, at the end of which are one or more extremely elongate brood cells. The cells were normally found to contain one or more eggs, each in a small empty pocket entirely within the provisions of soft pollen, which completely filled the cell. The attachment of the egg to the provisions is described, as is the egg itself.

The first four larval instars remain attached to the provisions while the elongate fifth (final larval) instar is free from the provisions and starts defecating while still eating the food, which gradually intermixes with fecal pellets. Toward the end of defecation, larvae start spinning strands of silk to form cocoons. After finishing spinning, larvae enter diapause, becoming quiescent over a period of more than a week. However, when in diapause, they still react to touch by curling and uncurling their bodies unlike totally quiescent diapausing larvae of most bees. Cocoon structure and function are described.

Throughout the paper, aspects of nesting biology of this species are compared with those of other lithurgines. New details concerning the cocoon of Trichothurgus dubius (Sichel) are presented, and ovarian statistics for Lithurgopsis apicalis are appended.