When at war with the AI it sends an escort or two along with a transport directly for your planets. From playing I have noticed if I have the paranoid ability, two free drones at starbases/planets/shipyards, the AI will attack a planet, defeat the drones, and then stop. The AI will not attempt to attack the planet again in that same turn. Drones are replaced each turn so the AI will attack, win, and do nothing. They seem to never conquer a planet, just continually attack, defeat drones, wait until next turn to attack again. I assume drones will stay as they are so I think the AI needs some tweaking in regards to invading planets of a race with the ability 'Paranoid.'