Bacteria colonize the animal gut, and they have an important role in host fitness. But, how the symbiotic bacteria recognize their specific niche and maintain colonization is not well understood. In this work, Gutiérrez-García et al. show that the commensal bacterium Lactiplantibacillus plantarum specifically recognizes the foregut of the fruit fly as its physical niche via sugar-binding adhesins. The authors used single-bacterial cell tracking in living Drosophila melanogaster and showed that L. plantarum exhibits high-affinity binding in the foregut of the fly and not in other areas of the gut. They noticed that evolved bacterial populations that had been passaged in a rich liquid medium had a colonization defect. This defect was linked to the loss of a gene cluster region, which the authors termed the ‘colonization island’ and is located on a linear plasmid. The cluster contains open reading frames for serine-rich repeat protein adhesins (SRRPs) and auxiliary SRRP secretion genes. Microscopy experiments revealed the presence of filamentous structures on the bacterial surface, and knockdown experiments confirmed that SrpA and SrpB are necessary for strong colonization. Moreover, the data suggested that N-acetyl glucosamine is the host factor that the bacterial adhesins bind to. Finally, the authors reported that the colonization island is conserved across the host-associated Firmicutes phylum, which suggests that this adhesin-mediated mechanism of niche recognition is widespread.