Life history theory predicts that the intensity of selection will decline as individuals age; thus, adaptive traits should decrease during post-reproductive stages. To test this prediction, I measured several potential fitness variables in adult female crab spiders [Misumena vatia (Clerck 1757): Thomisidae]: maximum mass before laying, mass after laying, mass at release into hunting site, carapace width, and days since egg-laying upon A) daily rate of loss in mass after egg-laying while guarding a brood and B) daily rate of gain in mass after release into a rich hunting site. These individuals were members of a normally semelparous population guarding their nests without feeding for 1–26 days past egg-laying. Rate of decline in mass of the spiders slowed significantly over time (P < 0.01), and large individuals lost mass relatively faster than smaller ones (P < 0.05), but no other tested variables affected their rate of loss in mass. However, none of the above-noted variables significantly affected their rate of gain in mass after release into the hunting site. None of these individuals likely produced a second brood. The scarcity of relationships among variables measured, especially those following release into the rich hunting site, is consistent with these individuals experiencing little or no direct selection for fitness-enhancing traits subsequent to egg-laying. The exceptions noted for the guarding period probably resulted directly from success at an earlier life stage.