Thousands I'm guessing.
Okay, then "some" is rather unclear, and a pretty major understatement. That's the equivalent of several villages of humanoids. And it would have taken.. well, an army of humanoids roaming the hivemind's lands for days to weeks, destroying nests of the things, engaging in pitched battles.
So, they didn't "kill some". They went to bloody war with them.
Which is fine, but would have been nice for the scale to be clear up front.
They don't plan on farming humans they're protein right here and now. If they say depopulate northern Gaul they have enough land to return to previous behavior.
I think we often have language use issues. Earlier, you said the queens think the humanoids are the resources - implying the humanoids are supposed to be what keeps the hivemind from starving. Now, you mean the land are the real resources.
PC actions can prevent this.
Yes, but I betcha my solution isn't yours.
We do agriculture because it produces far more food per square km than hunting and gathering. If the basic problem is now the insects have too high a population for their land to support, they either get more land, or increase the amount of food they get from their land.
So, some humanoids go in and farm, increasing the output of the land several times over, easily supporting themselves, with extra for the hivemind
Or... go in and kill the queens. That's the usual adventurer way to handle such things.