The physiological bases for major ontogenetic differences in developmental patterns of closely related social and solitary huntsman spiders (Sparassidae: Deleninae) were explored in two social and four solitary species. The three group-living huntsman spiders, D. cancerides, D. lapidicola and D. melanochelis, develop differently from all other known solitary Delenine spiders. The social species have a non-feeding 2nd instar, while solitary huntsman feed as 2nd instars. To determine the physiological basis of these differences, we compared egg size and clutch size; lipid, carbohydrate, and protein content of yolk; standard metabolic rate; and development time. Our results show that social species do spend a longer period of time as non-feeders and that they have larger eggs and maintain low metabolic rates during their non-feeding instars, which may enable the social spiderlings to remain non-feeding. We discuss the implications of developmental heterochrony on the evolution of sociality in spiders.