In popular knowledge, ant societies are an amazing example of animal collaboration. A working-together society full of brave actions. Less known are examples of working-against society full of shabby actions.
Consider the spectacular Polyergus, the Amazon ant, the queen of which penetrates into the nest of Formica species, kills the original queen, and subordinate existing workers to serve her and her own species. The original Formica ants become literally their slaves: the kids of Polyergus (warriors with huuge mandibules) are so big that they are unable to feed themselves. They need their Formica slaves to feed them. And, since the original queen is dead, they have to find some fresh supplies of new Formica workers somewhere every now and again, in order to survive. So, in the evenings they go off out of the nest on a wild ride searching for other Formica nests, fight them, take out their larvae, bring them home to their Formica slaves who then take care of them and thus raise more and more slaves for their "cruel" Polyergus masters.
This last part was a bit untought of, as it were, by Anergates, the queen of which does not produce any workers at all. She gives birth only to queens and males. So, when she penetrates into the nest of the Tetramorium ant, and kills the host queen (some parasitic species also try to make a deal with the host queen so that they can live side by side with the host queen in the same nest), then when all the host Tetramorium workers slowly die off, the whole Anergates colony dies as well. There are simply no more workers left to get food.
Or take tiny Diplorhoptrum ant, who lives inside the nest of a bigger Lasius species, viciously stealing food from them from time to time. And, when Lasius soldiers get finally angry and rush after them to get them, Diplorhoptrum simply hides into their tiny narrow corridors inside Lasius nest, where the bigger Lasius cannot penetrate because of their size. Tiny but smart, Diplorhoptrum!