No they won't.
When the aliens come, they won't eat us.
Wanna know why?
Why don't we eat each other?
What's to prevent me from eating the nice lady next door? I'm sure she tastes nice and is nice and nutritious.
Because she's a fellow person.
Why won't the aliens eat us? Because we are fellow people.
They won't eat a fellow person.
Would we eat someone's pet cow?
Then why would they eat a species that they can clearly see has built a civilization?
When the aliens come, they won't eat us.
To have the capacity to travel to another star system, they would have to be a reasonably advanced civilization mentally. At least close to our level. If not much higher, like Ming China or the Baghdad Caliphate. They won't eat a fellow intelligent being.
When the aliens come, they won't eat us.
Not even if you make yourself a major pest.
And you can bet on that.
Sincerely,
David S. Annderson
P.S. Maybe they're already here, but they have a prime directive that keeps them from interfering with our civilization. If we came up with the Prime Directive, they could have too. That would explain a lot about the nature of many UFO sightings that have not been naturally explained! (there are a few that are yet unexplained... who knows?) And I don't think that the idea is so farfetched... hey, we'd explore another planet that had life, why wouldn't they?
(If it was practical for them to reach us. Travel among the stars is very difficult- the distances are huge!)
P.P.S. If they never come, that's why- not because they aren't out there, but because the distances between the stars are so huge that it's too difficult for them to come this far! Who knows how far it is to the next star system that is the source of a civilization? It could be hundreds of light years! And if there is no way around the speed of light, it would take hundreds of years to get here! But they're out there! Our planet can't be the only one that has evolved intelligent life!
P.P.P.S. And if they were in a survival situation, the alien from the species they have just made contact with would be the last person they would eat!