Laboratory cultures of larvae of the wax moth Galleria mellonella show drastically increased temperatures a few days after the start of cultures. To examine this phenomenon, we performed direct calorimetric measurements on isolated eggs and larvae of different larval stages. Fourth and fifth instar larvae have significantly increased mass-specific heat production rates (up to 160 mW g(-1)). These high heat production rates are obviously the reason for the increased temperatures in wax moth cultures. In addition to these results, larvae were reared successfully in the measuring chambers of the calorimeters in long-time experiments, and power-time curves were obtained continuously for the whole period of larval development (up to 40 days).