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The larvae of the North African winter breeders Broscus laevigatus and Orthomus atlanticus survive a temperature of 30° C and a relative atmospheric humidity of 75% only briefly. The first larval instar of O. atlanticus is particularly sensitive to dehydration. It does not live longer than the corresponding larval instar of the Central European species Pterostichus angustatus Dft.Examinations at a temperature of 20° C and a relative atmospheric humidity of 75% proved that the first larval instar of Br. laevigatus is well adapted to these conditions and on average remains alive for 121.7 hours, as against 19.6 hours at a temperature of 30° C. This is regarded as adaptability to the short periods of drought which still occur at the beginning of the rainy season. In their first stage the larvae of O. atlanticus die after as little as 4.5 hours.The two species develop at a low temperature which corresponds to the average winter temperature in the Cyrenaika (Libya, North Africa). Susceptibility to drought at high temperatures and the absence of the low temperatures they need for their development prevent Br. laevigatus and O. atlanticus from breeding during the North African summer.As the larvae of O. atlanticus in their first stage of development are susceptible to dehydration, reproduction in this species is mainly limited to the winter. Its different stages of development withstand high temperatures better than those of B. laevigatus. On account to the poor adaptability of its larval stages to high temperatures B. laevigatus is forced to propagate during the winter. Low temperatures (14° C) during the first larval instars accelerate the development of the third instar of the two species at a temperature of 20° C and reduce the mortality rate of O. atlanticus considerably. The accelerated development caused by low temperatures reflects in a somewhat lesser degree the larval diapause of the autumn breeders that live in the temperature zones.