The life stages of Sisyra pedderensis are described and statistical data from laboratory rearing experiments discussed. Novel sampling methods were used to obtain pupae from the field since adults were not attracted to black lights and the larval life cycle closed in the laboratory. The diel cycles of egg eclosion, full-fed larval emergence from aquatic habitats, and adult emergence are examined and illustrated. Morphological data are provided to identify the three larval instars. A comprehensive comparison of the biology of S. pedderensis and closely related overseas species is made. In Lake Pedder, this species of spongillafly was proved to be bivoltine, with overwintering larvae becoming imagines in early summer which was followed by a single summer generation.