Tenebrio molitor gained recognition for its nutritional value for human and/or animal consumption, its utilization as a model species in research studies, and its ability to degrade many types of plastics. However, it is a stored-product pest infesting a wide range of commodities in storages. The impact of temperature on the development of T. molitor was evaluated, taking into account confounding effects of other covariates such as developmental stage and larval instar. The time for larval development was longer at 22.5 °C than at 25 °C, 27.5 °C, and 30 °C. Tenebrio molitor spent most of its lifetime as larva > egg, pupa, since the outcome of our model inference resulted that the estimated probability of longer duration in larvae is approximately 25.5 times higher compared to eggs and pupae, and passed through 26 instars before it became pupa. Duration of larval instars increased significantly up to L22 and then decreased until L26. Among larval instars, L22 exhibited the highest developmental duration while the lowest was recorded for L1. These findings enhance the knowledge about the biology of T. molitor, leading to precise decisions for its successful culture.