Ant colonies are a hub of diverse interactions that are affected by a multitude of factors, such as colony members, external environment, and possibly the symbiotic bacteria that live within individual colony members. While symbiotic microbes are well-known to manipulate the physiology, ecology and evolutionary biology of their solitary hosts, we have limited understanding of their effects on the biology of social insects such as ants. Wolbachia, a maternally-inherited endosymbiont, is the most widespread insect endosymbiont. It manipulates host reproduction and confers fitness benefits to the host to favor its own vertical transmission. While Wolbachia is known to manipulate the reproductive biology of their solitary hosts, we know practically nothing about its effects in social species. In my thesis, I have compared Wolbachia-infected and uninfected colonies of the pharaoh ant, Monomorium pharaonis. I show that Wolbachia-infected colonies have higher colony growth and reproductive investment that arise due to individual-level differences in the queens. Wolbachia infection doesn’t seem to exact a detectable cost. Given these effects, Wolbachia can rapidly spread through colonies. Thus, Wolbachia infection rate has the potential increase even in natural populations, although this may be limited by the trade-offs that can become evident in certain conditions. Results from my thesis bridge a critical gap in our understanding of the effects of a widespread bacterial endosymbiont on the life history of a superorganism.