Method and apparatus for rearing insects is disclosed. Information concerning the physical and dietary needs of the insect as well as behavioral characteristics are utilized to maximize the number of larvae reared per unit surface area of diet and per unit of rearing area while minimizing the amount of labor and materials required. An enclosed rearing unit (1) is provided which can be located within an appropriate environment for rearing the insects. There are three sections within the rearing unit: 1) a diet space (2), 2) a larval space (3), and 3) a frass space (4). The diet space (2) includes an appropriate diet medium for the insects. The larval space (3) is located below the diet space (2) and includes a series of vertical partitions (12) perpendicular to and in contact with or nearly in contact with the diet medium such that the insect larvae are able to disperse themselves over the partitions (12). The frass space (4) is located below the larval space (3) such that any frass collects within the frass space (4) as it is produced and does not interfere with the larval space (3) or the diet space (2). The rearing system can further include an emergence pan (30) including an outlet for allowing emerging adults to enter an oviposition cage. The emergence pan (30) replaces the frass collection pan (24) when all of the larvae have pupated. The rearing unit is turned upside down such that the emergence pan (30) is located above the larval space (3) and the diet space (2).