Background: A relationship between body size and longevity has long been appreciated within eukaryotes, especially vertebrates. Introduction: In general, large size is associated with increased longevity among species of mammals and birds but is associated with decreased longevity within individual species such as dogs and mice. In this study, we examined the relationship between measures of individual body size and longevity in a captive population of speckled cockroaches (Nauphoeta cineria). Method: Newly molted adults of both sexes were removed from a mass colony housed in multiple terraria and housed individually with food and water provided ad libitum for the duration of their lifespan. Thrice weekly, the status (i.e. live/dead) of individual cockroaches was noted for the duration of the study. Individuals found dead were weighed and measured to obtain body mass and morphometric measures and the age at the time of death was recorded. The relationship between body size and lifespan was assessed. Result: Contrary to what is commonly seen within vertebrates, large cockroaches were longer-lived than their smaller counterparts. Specifically, body mass, body length and pronotum width were all significantly correlated with the age at death in a mixed population of males and females (n = 94). In addition, we found that the longevity of a historically larger population in terms of both body mass and body length were significantly longer-lived than the population used in this study. Conclusion: These data indicate there is a significant interaction between body size and aging in this species and that increased size results in a survival advantage. There is evidence in the literature indicating that a positive relationship between size and longevity may be common in insects.

In the 1950’s Denham Harman proposed the Free Radical Theory of Aging whereby species lifespan and individual longevities are the consequence of free radical driven damage to biomolecules. This led to decades of research to ascertain the effect of altered antioxidant defense systems on aging and mortality in an array of species using reverse genetics and dietary manipulation. Within invertebrates, the data generally support the Free Radical Theory in that overexpression of antioxidant enzymes or dietary supplementation with antioxidant compounds increases longevity and resistance to oxidative damage. Likewise, genetic knockdown of antioxidant defenses generally shortens longevity within invertebrates. On the other hand, for endothermic vertebrates (i.e., birds and mammals) the results have been equivocal. Downregulation of antioxidant enzymes typically results in an increased oxidative burden, but without an appreciable effect on longevity, while dietary supplementation with antioxidants has little-to-no effect, at least at the concentrations used. Upregulation of antioxidant enzyme genes also fails to increase longevity in vertebrates most of the time. Interestingly, manipulating antioxidant defenses in fishes increases longevity in conjunction with reduced oxidative damage akin to what is seen in invertebrates. Since invertebrates and fishes are both exothermic this raises the possibility that the evolution of endothermy interferes with the ability of antioxidants to slow the aging process.