A prepupa is a non-feeding stage that occurs between the final feeding larval instar and the pupa. It is less common in Lepidoptera because most species pass relatively directly from feeding cessation to pupation. This paper describes the occurrence of such a stage in the thyridid moth, Calindoea trifascialis (Moore). The prepupa is primarily a functional designation based on attributes associated with an extended wandering phase. The distinctness of this stage was demarcated by observed changes in the integument at the transition point to the prepupa. It was also corroborated by morphometric comparisons of length and mass with the final feeding instar. Measures of head capsule width indicated a potential stage-based departure from the Brooks-Dyar rule. The model fit changed with the number of instars assigned to the life cycle and depending on whether the prepupa was considered as a distinct instar. In the latter case the deviation was marked; but with the prepupa excluded, the growth curves still hinted at compensatory adjustments to growth increment prior to the non-feeding period. Molting was cryptic as a result of the use of leaf shelters and the consumption of exuviae after ecdysis.