Like it was told before, slaves are expensive and inefficient compared to robots, let alone that they won't survive or function well in a planet with different gravity or climate or atmosphere.
I was kind of jokingly hinting at the existence of Wraiths from Stargate Atlantis lol... "feeding ground" was the clue.
What if for some strange reason, a culture advanced enough never developed robotics because of an abundance of slaves and their economy revolved around the procurement and habitat for them? I mean if there was a species that communicated telepathically, you wouldn't see inventions like the telephone. If the need isn't there, the technology might not get developed.
That's why when meeting an alien civilization for the first time, never presume anything, no matter how you perceive them to be! Like you, they've probably had billions of years to evolve in ways that are totally beyond our comprehension - so the normal greeting between two parties that meet for the first time may completely be an unique Earth-construct that is totally foreign to that alien civilization, let alone the entire Universe. Computers don't take the time to "greet" when they are connected for the first time - they just plow through with information that is instanteously converted. That alien civilization may use that method when they sense our presence... it's gonna be rough, for sure! Talk about being "screwed" to a new level. LOL