To evaluate sociality in small carpenter bees (Ceratina Latreille), we studied the life history and nesting biology of a common eastern North American species, Ceratina (Zadontomerus) calcarata Robertson. Pan-trap and nest collections throughout the active season (May to September 2006) were used to assess seasonal phenology and nesting biology of C. calcarata in southern Ontario. Adults overwintered in their natal nests. Males emerged in early May and occupied preexisting hollows in twigs and stems. Females emerged from hibernacula 2 weeks later, founding new nests. Nest founding and provisioning occurred throughout the spring; females remained with developing brood through the summer. Complete nests contained, on average, 6.9 offspring, with egg-to-adult development averaging 46 days. Ceratina calcarata is subsocial rather than solitary: mothers are long-lived and nest-loyal, and care for offspring from egg to adulthood. Subsociality is found in all behaviourally classified small carpenter bees, while some species cross the boundary into social life, making Ceratina an important genus for the study of the transition between solitary and social life.