Humans are fucking terrifying.

Alien 1: so tell me about this new species you've found

Alien 2: well it's in a kind of backwater planet of a backwater galaxy so they haven't made contact with any other sentient species. Only one sentient species on the planet. Couple of almost-sentient though, but one has achieved dominance.

Alien 1: not uncommon. Tell me about them.

Alien 2: they're terrifying.

Alien 1: really?

Alien 2: they breed and expand like a virus, taking over every geographic area they enter.

Alien 1: they have large litters of children then?

Alien 2: no, relatively few.

Alien 1: how do they take over--

Alien 2: they. kill. everything.

Alien 1: they wha--

Alien 2: they were responsible for multiple mass extinctions before they developed writing.

Alien 1: Oh my. How do they hunt?

Alien 2: They chase their prey.

Alien 1: Well, yes, but how?

Alien 2: They chase their prey until it drops from exhaustion. They do not stop.

Alien 1: Well that's frightening.

Alien 2: Oh and they're pack hunters.

Alien 1: That just got worse.

Alien 2: They managed to quickly discover all the poisonous plants and prey in their area.

Alien 1: Ah, so they're intelli--

Alien 2: And they consumed them en masse.

Alien 1: ...

Alien 2: for fun.

Alien 1: we should probably destroy their planet.

Alien 2: in self-defense.