The life histories of three darkling beetle populations were studied using pitfall traps and ovarian development in females from field samples and laboratory rearing during three years in typical Mediterranean grassland and pinewood study areas. One population presented a “one-year life cycle, overwintering as larvae”(Micrositus ulyssiponensisGermar), characterized by high adult fecundity and egg viability, emergence of new beetles in spring, ovarian maturation at the beginning of summer, and egg laying toward the end of summer and in autumn. A second group of populations was characterized by a “two-year life cycle, larvae and adult overwintering”(Pimelia costataWaltl andTentyria platycepsStevens). In this case, darkling beetles are maxithermics because they seek out particular thermal microhabitats that allow them to stabilize body temperatures at high levels (newly emerged beetles occurred in midsummer, reproductive periods from spring to the end of the summer of the following year, and high adult fecundity and egg viability were observed only in summer.