Animals generally have no qualms at all about killing or even just mutilating other animals. It often happens almost by accident - two animals might be playing together, one gets spooked, and it instinctively attacks and perhaps even kills the other one - this is commonly seen with people who befriend large predators, such as tigers in the infamous Siegfried and Roy tragedy, but it also happens a lot wherever animals interact with each other.

Specifically in regards to your ant example, anteaters and bears often bring similar levels of destruction to ant nests. And cats and other small predators often hunt just for the fun of it, killing but not eating their prey.

On the more purely painful evil side, invertebrates often consume their prey alive, inflicting agonizing deaths with no issues on whatever they may be eating. Plenty of vertebrates kill and consume their babies, especially when frightened. They also often abandon old and weak members of their packs, leaving them to die of hunger or cold or similar deaths.

This is not meant as some indictment of the animal kingdom - people do all of this too, of course; and have since time immemorial. It's just to show that, if we apply human moral standards to the animal kingdom, it's fair to call them violent, and yes, even much more violent than the average modern human.