A continuous sieving apparatus (2) is described. The continuous sieving apparatus (2) includes an inclined sieve surface (22) attached to a wall (48). The inclined sieve surface (22) is inclined with respect to a horizontal axis for pupae to continuously flow across down the incline. A set of openings (62) is formed in the sieve surface (22) so as to define a set of pathways extending through the sieve surface. The set of opening (62) are defined by a length dimension (72) that is greater than a width dimension (70). When the inclined sieve surface (22) is submerged in a liquid, a first pupa (90a) having a first cephalothorax width (91) that is less than the width dimension (70) is free to move through any one of the set of openings, and a second pupa (90b) having a second cephalothorax width (91) that is greater than the width dimension (70) is prevented from moving through the set of openings (62).