ABSTRACTLaboratory studies demonstrate that the gut microbiome can regulate host anxiety and exploratory behaviour. While this has implications for human health, it could have ecological and evolutionary implications for wild populations, a hitherto untested hypothesis. We tested whether the microbiome can directly modulate host behaviour and thereby affect life history in wild mice (Peromyscus maniculatus) and voles (Myodes gapperi). We compared the microbiome composition, exploration and anxiety behaviours, and home range of mice and voles before and after chronic antibiotic treatment and measured survival during treatment. Treated animals had lower diversity and relative abundance of most bacterial phyla save for Proteobacteria which increased in relative abundance. In mice, antibiotic treatment increased exploration and decreased home range without impacting survival. In voles, it lowered survival such that we could not test its effect on behaviour. Therefore, the microbiome can directly impact behaviour and host life history in the wild.