During the warm season the larvae of Pyrrhocoris apterus select in their natural habitats places with temperatures which do not exceed 24°C on average even at the hours of maximum sunshine. At the same time other places of their habitats have temperatures up to 50°C. This active behavioral selection of the microclimate regulates the speed of P. apterus development and entertains the monovoltine cycle in climatic, conditions of Central Europe. A less rigorous choice of the microclimate, even when higher temperatures were tolerated and the development was not disturbed by them, would cause the disturbance of the monovoltine cycle and would probably endanger the survival of the population.