The diversity of microbial symbiont population is increasingly recognized to play a key role in the host physiology and behavior. For social animals, such as primates and some insects, symbiotic microbes have been shown to be exchanged among individuals in their tight social interactions through sharing diet or habitats, resulting in an increase of consistency between microbiota among social partners. However, it is still difficult to disentangle how those social contexts affect the diversity of microbiota. Combining genomics and experimental approaches, we study several gut microbial communities of social insects from various ecological perspectives. In this talk, we will present some examples of unique properties of the communities associated with caste, diet, or habitat size.