Understanding the evolution and maintenance of cooperation is one of the major challenges in biology and is epitomised by the eusocial insects, which Darwin even considered to be potentially fatal to his theory of natural selection. Hamilton’s seminal papers revolutionised our understanding of evolution by explaining cooperation in social insect societies via kin selection, where individuals gain fitness by helping their relatives. But, in the absence of an overarching manager, how is it decided who does what tasks in these cooperative societies? Most biological research considers individual animals as discrete entities, however they in fact host a plethora of symbiotic microbes that can have significant beneficial or parasitic effects on their hosts. The importance of these symbioses is now beginning to be understood - gut microbiota have been found to affect, and be affected by behaviour and the expression of associated genes in different animals. Gut bacteria and behaviour in social insects are known to be influenced by many of the same factors (e.g. age), however, the relationship between microbial associations, sociality and division of labour, remains almost entirely unexplored. To address this gap, this project will investigate the relationship between microbial communities and the evolution of sociality, individual behaviour and division of labour, and the role in these of DNA-methylation-mediated effects. This will be achieved by sequencing and characterising the gut bacteria community and epigenetic architecture of workers performing different behaviours, experimentally manipulating the microbe communities, and also characterising individuals with different social phenotypes from a single population. This project will provide important insights into the bidirectional relationships between symbionts and division of labour, and the associated training will provide a step-change in my expertise as a scientist.