Blochmannia is a vertically transmitted obligate bacterial symbiont of ants within the tribe Camponotini (Formicidae: Formicinae), hosted in specialized cells (bacteriocytes) of the ant midgut epithelium. Genomic comparisons of Blochmannia with other insect symbionts suggest that the symbiosis may have started with ants tending sap-feeding insects. However, the possible transitions of Blochmannia from mutualist of sap-feeding insects to vertically transmitted organelle-like symbiont of ants

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... not been formally discussed. Here I propose hypotheses supporting the idea that the ant brood may have had a prominent role in this process. This is mainly because: 1) microbes are more likely to reach the midgut in larvae rather than in adults; 2) bacteriocytes possibly allowed the midgut lumen-dwelling ancestor of Blochmannia to survive gut purging at the onset of the ant pupation, extending its nutritional benefits to metamorphosis; 3) adult ants do not need the nutritional benefits of Blochmannia. Investigating the biology of Camponotini sister taxa may provide further cues regarding the evolution of the symbiosis.