To find out what kinds of microbes live in the nooks and crannies of the ocean crust, researchers dropped sterilized rocks into plugged drill holes. The biofilms that grew on the rocks were somewhat different from organisms that swim in the fluids, showing that both communities are important to our understanding of this giant subsurface ecosystem. Featuring the recent paper Ecology of Subseafloor Crustal Biofilms (Frontiers in Microbiology, C-DEBI Contribution 391).