Continued from Wednesday.
The boginki require hosts for their eggs. They possess a venom that paralyzes in small doses and causes cellular breakdown in larger doses, and they use it for its former effect after choosing a target. Captured and paralyzed, the boginka's victim is helpless to resist as dozens of eggs are implanted deep in the flesh. They will nourish themselves on their host, who will be sustained as the adult boginka regularly injects them with a nutrient slurry. The larvae that are the earliest to rouse themselves (and are the most fit) will make their way to the brain, which they will consume and... replace. They merge with (or devour, depending on how you look at it) each other and plug into the nervous system, between these two actions drastically increasing their intelligence. Very soon, they will begin secreting a counter to the venom in their host and be able to secure food on their own.
The other larvae, meanwhile, are left in the cold as soon as their fitter siblings have begun to merge with each other. Early bird stays a worm (or quivering gestalt of many worms) and everyone else better boot out. Which they do. Here they are fed more directly by their parent with whatever is at hand and edible (even its own flesh, if necessary) until they pupate and assume their adult form. Unlike their siblings, left to their own devices they are doomed to remain nearly-mindless eating machines, but thankfully there is another role in life for them to fill.
The boginki communicate via pulses of sound too high and fast for humans (and even many other animals) to perceive. By the time that the their simple-minded siblings pupate, the brain-larvae are ready to use this system to receive information from their siblings when necessary but more importantly to send commands, which their siblings process as their own thoughts and obey to the letter. Together they form a dangerous team as the brain-larvae giving needed direction to their "soldiers," who are responsible for keeping the cycle going. Without the brain-larvae they would be no more than animals, but nevertheless remains that it is only through them that the brain-larvae, who never mature physically, can see any of their genetic material passed on, even if it must be by their siblings.
The brain-larvae use this ability to communicate with others like them, as well, and in many cases function like parts of a disparate hive mind that comes together here, then there, separating and rejoining in endless repetition. They are using this to achieve a unity of purpose now that, quite by chance, it has been proven to them that the outside world is, far from some kind of ghost-haunted Hell, a ripe breeding ground with room enough that they might forget whatever rivalries they now hold. When they consume the brain they take memories as well, and for as long as they took locals their sights were turned inward. The locals may have had memories, as confusing as they were to the boginki, of a world outside the wood, but it was clear that they felt as disinclined to join it as the boginki were. Everything else slipped through the cracks as the boginki struggled to understand what they were perceiving. That older brain-larvae would teach their siblings' children as the latter developed may have only compounded the difficulty, not lessened it, as they forced their own interpretations of the data that the young boginki were receiving.
But the Soviets had begun to hear rumors of dark things in the forests of Poland, and they sent agents to investigate. Some of them fell prey to the boginki, and the larvae that possessed these hosts were able to understood quite clearly the potential that was there. When they finally left the wood, greeted as men long-missing and presumed dead, they did so with a plan. They are moving slowly, perhaps, but their infiltration has survived the fall of the Soviet Union and they remain entrenched in Poland, slowly acquiring more positions of influence and coming to understand more and more just what they are capable of achieving. In time they will be ready to move beyond Poland, but they are patient. They will not move so quickly that they will reveal themselves, not when they have all the time in the world.