The world around us is full of microbes that influence both biotic and abiotic components of ecosystems. For instance, nitrogen-fixing bacteria enrich the soil1, and algae in marine ecosystems provide sustenance to a variety of organisms2,3. On the other hand, pathogenic bacteria cause diseases across trophic levels, changing the environment around them dramatically. Such interactions have been extensively studied for a long period of time. However, non-pathogenic host-bacterial associations also influence host physiology and even host behaviour4,5. For example, in mice, differences in gut bacterial communities determine utilization of specific dietary components and the propensity for diseases like obesity and diabetes6,7. Gut bacteria are also linked to several neurological disorders such as depression and anxiety8. Such dependence of animal hosts on their gut microbes is not limited to humans, but extends across the tree of life.