Inspired by TrEs-2b's Ant-hill species http://meta.worldbuilding.stackexchange.com/questions/3781/what-species-are-you-currently-designing/3794#3794
As well as this question How do I wage war against a collective consciousness?
Now that it is known how an ant-hill can be defeated but we do not know how do they fight! Would they gather as one giant collection of ant-hills, each with hundreds of thousands of ants, or each attacking on it's own?
A collective consciousness would be able to give instant orders and to place troops perfectly one by one, something that even a strategy games player often don't bother to do even by having the ability to pause the game. Also troops would have no hesitation to sacrifice themselves if that can be turned in a great advantage for the consciousness.
Again this is depending on the fact how the collective consciousness really work. (in example instant communication to all entities, or just a behaviour that favours the collective? I assume the foremost).
How do they fight? Like every army, they would place troops with weapons. Think at when SWAT breaks into a building, they already programmed that action and the criminal probably barely imagine what is going to really happen and how the troops are really moving, you see few individuals against a organized collective.
When someone gets killed you know roughly the position of who killed him, and you can send immediately some soldier from more appropriate positions. Coordinating ants to dig tunnels under enemies is also a breeze and most of the army would be organized into sparse clusters with solitaire scouts exploring the surroundings.
Modern armies approximate to a certain degree that concept (forts, outposts, headquarters), but then logistic coordination becomes a problem so we have to accept compromises. but a collective consciouses could do that in an almost perfect way without compromises because has no coordination problems.
Guerrilla is the most effective weapon, they would just allow their enemy to enter the territory and then face the logistic consequences of that, they don't even need to kill soldiers at all, just cut supplies and sabotage in a perfectly stealth fashion and enemies don't even know how many ants are facing.
Attacks would be coordinated in the moments in which troops are most vulnerable, they could retreat instantly as long as all soldiers are waken up, and attack when most of them sleep, making it really stressing and hard for soldiers.
As long as soldiers get used to a certain behaviour they could change behaviour (in example if every attack is followed by a Immediate retreat, then soldiers may no longer be willing to get out of bad and every attack, and that would be the perfect moment for the final strike).
Of course maybe you don't want such perfection otherwise the plot could become much more boring.
A) "Ancillary Justice" trilogy just won the Hugo/Nebula awards for covering exactly a collective consciousness at war with itself. Go read! :-)
B) For an ant-colony like collective specifically, I think the question is best asked "how do you wrestle with your own conscience?" Your brain is a collective consciousness -- various subsystems that each contribute to an overall view of the world that gets synthesized as one. Neurons just aren't allowed to wander apart, generally, and they don't ever operate in isolation from the rest of the collective. But human minds do get divided from themselves.
I would treat the ant colony at "war with itself" simply as insane... no longer doing what is needed to maintain the colony as a whole, but each ant simply not coordinating activity with the other ants. They don't even have to be particularly evil about it, just not aware of/subservient to the needs of the colony as a whole.
I also have my own idea on how they would do so. Being a big fan of the Warhammer 40.000 universe, I'll take two very different examples.
On the one hand, we have the Tyranids, which are basically giants swarms of insectoids creatures obeying to the Hive Mind.
Their main strategy in war is the good old mass assault tactic, sending millions after millions of small sized creatures to overrun most defences. But, it is not the only thing the Hive is using. There are some bigger creatures, used as walking tanks to destroy heavy fortifications, there are also tunneler creatures, flying ones, and all sort of things. So the mean they have on the battlefield are pretty common, the biggest difference is that these soldiers will never surrender, they will also never flee if under control. Meaning they will take enormous losses during any fight.
But how could they sustain that much losses ? Mostly by quick breeding and gestation. Another interesting thing is that most of these small soldiers can't eat. They got claws and fangs and mouths but do not eat things. Thus, once the fights is over, the smaller beings come back to somekind of gastric acid pit where they'll be digested and their biomass will be sent back to a ship, ready to be used to produce new warriors once more.
So, their soldiers are definitely reusables and don't have any word to say about it, apart from the bigger ones which have somekind of autonomy.
The most interesting thing with them is probably how they manage to maintain a link between them. The Hive mind needs somekind of relay to reach all of its minion. These are the most important creatures in the swarm, while these creatures are present, the small minions obey without a complain and everything is alright. But once these creatures are dead, the link between the Hive and the minions is cut, thus disrupting them greatly. It's generally a good way to deal with these creature, kill every Hive Mind relay, and the swarm will be quite easier to deal with.
These relay are also a strength as much as a weakness, for instance they allow some elements of the swarm to act independently, as infiltrators or assassins.
The second case in that universe is the one of the Necrons. Some might argue they do not have a real collective consciousness, and they are right, nonetheless they are using a lots of robots, and their base soldiers though they were human once, are now machines which must obey to their Overlord.
So for me it's quite like a collective consciousness in the fact that every Necrontyr apart from the high command will have almost no free-will and will mostly obey to any given order.
While the Tyranids fights in a very bestial way, with basic strategies from a predator hunting its prey, Necrontyrs are far more evolved and tends to use the fact their soldiers are soulless, emotionless and can react at the speed of a quantum processor to build powerful strategies.
Apart from the fact they master an impressive military technology (hey guys, look look we have the power to turn a star into a supernovae !) their tacticians can count on an impressive level of coordination. Even though they could gather in impressive big blocks of soldiers they tend to be organized in units, somehow inspired by the roman legion system, with centuries, cohort and legions.
Taking advantage of the fact they're mostly machines, their plans are made in multiple dimensions, using complex mathematical / physical concept, to the point the only other race that can really surprise the best Necrontyr strategist are the Orks since they are so dumb and acts in such an irrational way that their moves can't be predicted by science.
When facing Necrontyrs, you can count on enemy reinforcement joining the fight at the exact moment needed, and when seeing their soldiers withdrawing you can assume it's part of the overall plan.
Lastly, their soldiers do not have any voice emitters or stuff like that. So they're fighting in a perfectly disturbing silence, broken only by the sound of their weapons. Afterall, why would these minions with no will need a way to communicate by voice ?
I hope it'll help you creates your own Collective Consciousness and make it ready for war.
The Borg
I'm not too sure about insects, but I think we could draw parallels with Gene Roddenberry's Star Trek. More specifically the Borg. A collective consciousness that encounters the Federation more times than any other opponent (Save for perhaps the Klingons).
So what do we know about how they fight?
Firstly - The Borg seem to have no independent thought, but are instead controlled by a hive-mind/Queen system. Each time the Borg are faced, it is generally a single cube or, if there are a significantly large number of foes, multiple cubes. (We do see a Borg Sphere that seems to contain the Queen in VOY/TNG)
These cubes hold multiple Borg individuals that are active, but seem to have no notion of any job save for that they are assigned to (But that could be just because it's the silver screen) - If we infer from this that the orders the individual receives are from the Hive or the Queen; then they are absolute meaning total control.
So how would they fight a war?
Borg work very well as a large-number tactic. With their maneuverable ships and hit-and-run tactics they swarm enemy ships before they have a chance to retaliate, and then, to replenish any lost drones in the melee, they assimilate their opponents into the collective.
The Borg also adapt rapidly to their opponents, their shielding adjusting to deflect or absorb weapon fire within a few hits and, while and insectoid army may not be as quick, there's no denying you could think up a way that such a hive mind could get around enemy fire.
We can infer that, because the Hive mind has total control, there is no room for individual thought or experimentation, meaning no outside-the-box, hail-Mary plans, which leads to them seemingly being outmatched by the Federation ships.
In Conclusion
I think if you take inspiration from here you'd be close to what you're looking for. It's not an exact match as, the Borg are still humanoid and not insectoid, but it seems the closest relevant similarity I can think of at this time.
