I don't like bugs. Like, at all. This time of year especially, when I can't go a day without doing battle with a centipede or take out the trash without having to fight through a hundred slugs or be outside for more than five minutes without having half my blood drained by mosquitos. So seeing a bunch of tiny little hellions running amok just automatically made me root for their destruction.
And yes, I usually find myself compelled to root for the evil empire anyway, but this is even more so.