During Drosophila embryogenesis, the fertilized egg gives rise to larva, a system with multiple cell types, tissues, and organs. Oxygen is the only chemical which enters the system during this process, which is fuelled by maternally supplied stores of energy-rich molecules. We are probing the dynamics and regulation of energy utilization during embryogenesis, which can be contrasted with a burning candle, when all of the energy stored in the fuel is lost to the environment.