In the classic alien attack scenario, invaders try to overwhelm puny Earthlings by sheer force, as in "Independence Day." Sometimes, space villains use monstrous beasts to do their dirty work, such as in "Prometheus" or the Godzilla flick "Destroy All Monsters."
In the real world, invaders already swarm over the face of the Earth. Invasive species have devastated many ecosystems and cost humans billions of dollars in agricultural losses and infrastructure damage.
However, some wildlife, such as American birds that feast on invasive honeysuckle, have learned to turn invaders into appetizers. Humans too make prey of invasive species by hunting feral hogs and Burmese pythons and eating animals such as lionfish (shown here).