Well done for observing this. Yes, one of the ways in which the author of this dramatic short story presents the ants as an unstoppable foe is through frequent comparisons to soldiers performing armed manoeuvres. For example, consider the way in which the ants are described as they come forward and approach the defences as they first arrive:
The hostile army was approaching in perfect formation; no human battalions, however well drilled, could ever hope to rival the precision of that advance. Along a front that moved forward as uniformly as a straight line, the ants drew nearer and nearer to the water ditch. Then, whey they learned through their scouts the nature of the obstacle, the two outlying wings of the army detached themselves from teh main body and marched down the western and eastern sides of the ditch.
Clearly, using such comparisons serves to emphasise the massive threat that this hoard of ants represents to Leningen and his men. They show that they are superior to even a human army in terms of their teamwork, discipline and how they work together, almost telepathically, to overcome the defences that are before them.