Two biological phenomena (prolongation of life span with dietary restriction, and life shortening with reproductive activity) have been described in several species but treated separately. For captive female bowl and doily spiders (Frontinella pyramitela), data reported by Austad were analyzed in terms of food consumed. "Reproductive success" was defined; its rate of change could be directly equated to food intake. To describe life span, the specific rate of change of median longevity was noted to be negatively proportional to the specific rate of change of food intake. Both reproductive success and changes in median longevity are coupled to food intake in these female spiders, and can be described by quantitative expressions.