Most spiders are solitary and aggressive towards cohorts, but some have been found to live in groups and forage communally, even sharing in brood care. The benefits of group living outweigh the costs of inbreeding for these spiders, but how sociality has developed in arachnids is yet unknown. In this study I test the neoteny hypothesis for the origin of sociality in spiders in the Anelosimusgenus, which contains many of the known social spiders. The neoteny hypothesis predicts that due to retaining juvenile traits and maturing at an earlier morph, social spiders will have smaller body sizes than their solitary relatives. Using a novel phylogenetic tree of Anelosimusspecies and other outgroups, I used correlative ancestral reconstruction of traits along with analyses of variance to see if body size decreased with an increase in social level. The tree contained 8 evolutionary replicas of sociality (9 social species, 8 independent evolutions of sociality), therefore making it the perfect platform to test the neoteny hypothesis. There was no difference in body size between sociality levels, and the neoteny hypothesis was rejected. I did however, find evidence that social spiders have smaller clutch sizes, as well as a female-biased sex ratio. This supports the hypothesis that social species evolved small clutch sizes with more females to combat extreme oscillations in their population size, and tells us more about how their sociality may have come to be
