This is the fourth movie homage in a row! First, the Mummy, then Bodysnatchers, then King Kong, and now "Them" and its many imitators (Deadly Mantis, Black Scorpion, etc.). And with his unlimited special effects budget, Kirby does it better!
This is also the first two parter, and (I will argue) a story continued from an earlier issue: a step to the continuous monster stories that became The Marvel Age of Comics.
In the previous post I said how larger animals become weaker. I explained it because doubling height means four times strength but eight times weight. This story overcomes that problem through continuous growth: the force of each muscle (or equivalent) is increased because it is also pushing against itself as it grows. For example, imagine a leg that had no muscles at all: it could still push, simply by growing. And note that the giant ant does not do anything exceptional, it does not run or jump, it just leans on things.
Another advantage that mini-beasts have is their enormous variety. Their simplicity allows them to mutate very quickly, creating countless millions of kinds. Even if we allow for them weakening as they expand, some form can be discovered that would do whatever we need when scaled up.
For example, we could find a worm that did nothing but pull at the right scale. Sure, it would be weaker than a metal chain, it could make up for it by being thicker. its real advantage would be in its simplicity in creation. Anybody who needed a crane could carry it and the growth formula in his pocket, and then use sugar (or whatever the insect ate) to make it move into position. As Kirby explained, the real advantage was simplicity.
But wait, how does a serum allow ANY creature to grow? Kirby wisely leaves that unexplained. But he gives us a hint: he needs the sap of trees from just one place, Krakow. Remember Krakow? Where the alien water creature was destroyed? The water that soaked into the ground would be used by those trees. The scientist presumably learned everything he could about that event and put two and two together.
This also explains how the ant's brain learns so quickly: this is a continuation from the Gor-Kill story, where any suitable network (even water) can self-organise to become intelligent. So we not only have a two parter (almost a full issue) but a continuous story. Kirby is creating the Marvel Age of Comics.
Kirby the prophet
And finally, another warning against building life forms bigger and smarter than ourselves. It's happening now.