Kael reached the branch chokepoint six minutes before the first army ants arrived. The chokepoint was a four-inch section of the colony branch where a secondary branch junction had been removed years before, the cut ends sealed with resin, leaving a section with a smooth, narrow upper surface bordered by compressed resin seals.
At its narrowest, the traversable surface was exactly two ant-widths. An army ant raiding column, for all its numerical superiority, would arrive at this point in pairs.
The defense formation was already in position. Sixteen major workers in two-ant-deep ranks across the chokepoint width, the frontmost pair braced in the widest stance their anatomy allowed, mandibles forward. Behind them, six smaller workers assigned to chemical deployment — their abdomens loaded and ready, positioned just far enough back to spray forward past the defenders' bodies without risk of hitting their own nestmates.
Zara was managing the defensive structure from a position three feet back from the chokepoint, high enough on the branch surface to see both the defense formation and the approaching column on the trunk below. Kael took position at the chemical reserve relay — the line of workers passing fresh formic acid supply from the storage chambers in the pavilion to the deployment workers at the chokepoint.
In a sustained defense, relay speed was a limiting factor. He checked the relay spacing and repositioned two workers whose interval had been slightly too wide, closing the chain.
"Column contact in forty seconds," Zara announced.
The first army ant appeared at the base of the chokepoint approach — moving fast, following the pheromone trail of the colony's own chemical markers. It was slightly larger than Kael, darker in color, with the powerful, crushing mandibles of the army ant caste. It reached the leading defenders and the first combat engagement was immediate.
Army ants were aggressive by nature — their entire behavioral architecture was built around the assumption of numerical dominance, of forward momentum maintained by constant reinforcement from behind. The single army ant at the chokepoint fought with that same forward-drive assumption, pushing against the defenders with a force that Kael could read in the vibration pattern transmitted through the branch surface.
The defenders held. The two major workers at the front absorbed the pressure and returned it, their grip on the branch surface giving them a leverage advantage that the attacker, arriving at the top of a vertical surface without a fixed footing, could not match. The chemical deployment workers sprayed.
The formic acid hit the leading army ant at close range — a controlled burst directed at the head and thorax, the concentration at close application range significantly higher than what the army ants would have encountered in normal territorial marking. The effect was immediate: the leading ant stopped its forward push, redirected its movements laterally, and began the characteristic circular pattern of a chemically disrupted insect searching for orienting cues its senses could no longer reliably provide.
The second army ant arrived. And the third. And the fourth.
The chokepoint held them to two-at-a-time combat engagement. The defenders' established footing continued to provide the leverage advantage. The chemical deployment was systematic — short bursts timed to the attack cycles, conserving the formic acid supply rather than depleting it in a single sustained spray.
For forty minutes, the column pressed against the chokepoint and the colony held it. The relay chain that Kael managed delivered fresh chemical supply to the deployment workers fourteen times during that period. Three of the major workers at the front were replaced when their grip fatigue became apparent in their movement patterns, fresh defenders rotating forward from the second rank as the tired ones stepped back.
At minute forty-three, the column pressure began to change. Not a retreat — army ants did not retreat in the conventional sense. But the forward momentum diminished.
The density of arriving ants at the chokepoint base reduced. The chemical disruption signals being carried back through the column by retreating front units were doing their work, propagating through the army's chemical communication network: the upward route was costly, the target was defended, the formic acid concentration was high enough to cause significant sensory disruption. At minute fifty-one, the leading elements turned back down the trunk.
Within eight minutes the last army ant had descended below the colony's chemical boundary markers. Kael released the relay chain position and sat on the branch surface for a moment. The chokepoint was intact. All sixteen major workers in the defense formation were still present, though three showed the particular movement pattern of significant physical strain.
The chemical reserves had been reduced to approximately forty percent of their pre-defense level — workable for normal colony operations, inadequate for another sustained engagement of the same scale. He would need to note that in his post-action report. Chemical reserve replenishment: high priority.
He started writing it in his head as he walked back toward the pavilion.