Data on breeding and survival were obtained by random sampling from several natural populations of Agonum fuliginosum and A. thoreyi (Carabidae: Coleoptera). The relationship between breeding and survival was examined also in enclosed experimental field populations of the first species. The hypothesis was tested that, other mortality factors being of equal intensity, the survival of adult females, from near the end of one breeding season to the start of the next, is inversely proportional to the amount of reproduction done in that first breeding season. It is suggested that this is one of the compensatory mechanisms leading to population stability in Carabidae and may be widespread in other insects. It is pointed out that the expected influence of natural selection upon life history phenomena may be quite different when actual, rather than potential, population changes are considered.