How to conquer a stone age planet as devouring swarm?

I am playing as devouring swarm and found a nice Gaia planet in my borders, which is inhabited by some stone age primitives. So I invaded the planet with my armies in order to colonize it and get a nice stone age snack.

But as it turns out this is not how it works. After the invasion the planet has an "Occupied" marker, but I have no control over the planet and I also can not eat the primitives. My Native Interference policy is set to "unrestricted".

Here is how it looks like:

Is there anything else I can do get full control over this planet right away or do I maybe need to wait until they advance to the bronze age?

Apparently, its not possible to devour primitives with a devouring swarm in the current version of the game (2.2.4). I also tried with more advanced primitives, but got the same result.

The only option to colonize such a planet at the moment is to conduct orbital bombardment it until all primitive pops are dead. After that you get the colonize option.