While in the humanities and social sciences at large we can observe posthumanist developments that engage with the microbiome, microbes are still not a major topic of discussion within environmental ethics. That the environmental ethics literature has not engaged extensively with this topic is surprising considering the range of theoretical challenges (and opportunities) it poses for environmental theorising. So, this paper is ‘looking through the microscope’ from an environmental ethics angle in order to see how these little beings challenge what (...) we consider to be ethically relevant and how we conduct moral theorising. Especially interesting is how a focus on microbes can simultaneously support and challenge individualist biocentric intuitions and theories, which attribute moral standing to (some) microbes. Accordingly, the main aim of this paper is to lay out crucial aspects of these challenges and present some initial arguments about why not all of them pose a serious threat to biocentric theorising—including biocentric theories of interspecies justice. The three challenges discussed are (1) the moral significance challenge, (2) the self-defence predicament, and (3) undermining individualist biocentric intuitions. (shrink)