Pheromones... (spoilers)
So we know the Carryx are receptive to pheromones, not surprising for bug-like aliens, and we can see the direct reaction they have to them as well (literally changing their physiological shapes and essential nature)...
>!I noticed on my recent re-read in TFoB, 3 separate occasions The Swarm explicitly uses (or mentions using) pheromones, as some mechanism to help it sway other humans' opinions on things. The really peculiar part: The effect of its use is entirely unacknowledged, as if there is none. In TMoG, The swarm mentions twice about pheromones, once for shifting its awareness to them, once contemplating "disabling the host's pheromone receptor sites".!<
>!Well, you see, the thing is... Humans don't respond to pheromones, anyone with a Biology Degree (*cough* Daniel Abraham *cough*) could tell you that. We inherently lack a vomeronasal organ, the primary anatomical structure that processes pheromones in other mammals. For the mentions of the swarm actually using pheromones in TFoB, the closest to even acknowledging is Jessyn's internal remarks that "She [Clae] smelled vaguely of spice".!<
>!I've already been batting around the hypothesis that there might be some link between The Swarm (and by proxy, Livesuits/Deathless/etc) and the private creches, I almost think this might be another clue too. Why would The Swarm be so insistent on using a mechanism of social influence on a species that absolutely doesn't respond to chemical signals, outside of noticing the smell? Pair that with the fact that The Swarm (and Livesuits) literally change the host body's physical structure to suit it's current needs, i.e. its "essential nature". Really intriguing if this is intentional, and/or a clue of a causal link. !<