The slugs in Robert Heinlein's story The Puppet Masters appear to only be able to communicate via "conference". The delays in their strategy appears to suggest that it takes a while for information to propagate through the "hive". But is there a "hive mind"?
How are decisions made? For example, how did they make the decision to grow a carapace to protect themselves against squishing?
Heinlein addressed this to some extent in the book. He outlined three means of communication, one of which is a version of another. The slugs can communicate from host to host, either directly or long-distance. They could communicate from ship to ship or ship to base, which would appear to also be host-to-host communication. And they could communicate via slug-to-slug conference.
In chapter eight, he writes:
One of the disadvantages we worked under in serving our masters-or perhaps I should say one of the disadvantages our masters worked under-was the difficulty of long-distance communication. It was limited to what human hosts could say in human speech over ordinary communication channels, and was further limited, unless the channel was secured throughout, to conventionalized code messages such as the one I had sent ordering the first two shipments of masters. Oh, no doubt the masters could communicate ship-to-ship and probably ship-to-home-base, but there was no ship nearby; this city had been stormed as a prize-of-opportunity, as a direct result of my raid on Des Moines in my previous life.
Such communication through servants was almost certainly not adequate to the purposes of the masters; they seemed to need frequent direct body-to-body conference to coordinate their actions. I am no expert in exotic psychologies; some of those who are maintain that the parasites are not discrete individuals, but cells of a larger organism, in which case-but why go on? They seemed to need direct-contact conferences.
He also suggests that each slug may be a cell of a larger organism. From chapter nineteen:
They did do some direct experimentation which raised my opinion of them a little. Vargas ordered brought in a baboon who was wearing a slug and had him introduced into the cage with the gibbons and the chimps. Up to then the gibbons had been acting like gibbons, grooming each other and such, except that they seemed rather quiet-and kept a sharp eye on our movements. As soon as the newcomer was dumped in they gathered in a ring facing outwards and went into direct conference, slug to slug. McIlvaine jabbed his finger excitedly at them. "You see? You see? Conference is not for reproduction, but for exchange of memory. The organism, temporarily divided, has now re-identified itself."
I could have told him the same thing without the double talk; a master who has been out of touch always gets into direct conference as soon as possible.
While he doesn't specifically state how the decision to grow an armored carapace was made, it is reasonable to suppose that it was made by the slug super-organism. It may have exchanged memory slowly, but it did learn and adapt.
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It's not clear that the slugs were a single entity or that they/it thought or made decisions at all
The book opens with this statement:
Were they truly intelligent? By themselves, that is? I don’t know and I don’t know how we can ever find out.
If they were not truly intelligent, I hope I never live to see us tangle with anything at all like them which is intelligent. I know who will lose. Me. You. The so-called human race.
It is certain that the slugs use knowledge from their hosts - "The Old Man" knows how to manipulate his son, Mary is as a little girl not worth enslaving because she is (among other things) "ignorant."
There is no evidence that the slugs have any knowledge of their own (though some scientists postulate they have a "group consciousness," there is no proof of that) - the only powers that we are certain they have is an ability to coerce humans into aiding their continued existence and a desire to spread, and non-intelligent viruses have that. They travel in spaceships built by their previous victims (the titanian "elfs") and use human language to communicate under most circumstances.
McIlvaine the scientist suggests that "direct conference" spreads information between the slugs, but Sam doesn't seem to gain any knowledge aside from a vague image of Titan from his conferences. The frequent desire for direct conference may simply be a mating urge.
Even the development of a carapace might be a natural part of the slug lifecycle that arises after sufficient time to acclimate to a new body form.
