How convenient
To have an enemy that was not only not human, but also ugly
and seriously destructive. Removes the guilt factor.
But I wonder how long they expected to last if they wiped out
everything in their paths? Even with a lot of viable planets,
eventually you better lighten up on the wanton consumption
or there will be nothing left to eat but each other.
Maybe they would eventually become like the Vikings - even
they settled down and became citizens and farmers after ages
of maurading. The Bugs did have some Smart Ones after all.
Or maybe alien minds work in mysterious ways beyond our
ideas of logic.
Or maybe it was a work of fiction.