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Story starts with a guy buying a terrarium with 4 groups of beetle-like insects brought and installed in his own house by an alien race. A different color each. Each tribe were supposed to start a kind of colony on its share of the terrarium and sooner or later they were supposed to fight small strategic wars between them. They also changed its shape as they developed stronger.
The owner, against recommendations, is not patient enough to wait and starts to force such fights. Things go terrible wrong and one of the groups, I think it was the weakest yellow colored ones, get out of the container and he kills them. And everything goes downhill after that, as the beetles hate him and he actually has to fight them when they get free.
The yellow ones actually fully developed far from the house to be exactly like the aliens. It's just that the aliens didn't considered them as their offspring because they were way very underdeveloped if kept inside the terrarium.