I think they are the puppets of demons (aka evil spirits, aka fallen angels). Demons and their master Satan have long existed to tempt humans to sin, and this has been accomplished by keeping themselves hidden. If they become well known and easily seen, people will be able to start fighting back against demon induced temptations. So they have hidden themselves for thousands of years, acting subliminally to influence people's thoughts to cause them to commit sins.
Within the last hundred years though, one of them got careless and accidentally allowed itself to be seen by an airplane pilot. A UFO report was made by that pilot. The object was a blob of light without an easily definable shape. That glowing light seen by the airplane pilot was literally the actual supernatural energy being, the demon spirit itself (not any kind of spaceship). Ever since then, people have been reporting seeing flying aircraft with an actual solid physical appearance (often times with many lights, but not merely glowing lights by themselves in the sky). What is going on here is demons trying to debunk the original demon siting, by convincing everyone that the original sighting was just an alien spaceship siting, by the demons now going around and causing a bunch of alien spaceships to appear in the sky. By doing so, the demons intend to convince everyone that no demon has ever been seen, and thereby continue to hide their existence.
How are demons accomplishing this? They are creating spaceships. Using their supernatural powers, they materialize actual working spacecraft, and alien puppets. Why make them actual working craft rather than just empty metal shells? The craft are made as actual working craft so that if they should get shot down, humans will find an actual working craft and believe it to be of alien design. If they were just empty metal shells, people would know that it was being flown supernaturally, revealing the fact demons built them, and thus revealing the existence of demons, which is something that demons are trying to avoid. Why the alien puppets? Well they need something that looks like a living being be inside the craft, or else if it got shot down, people would see nobody in the pilot's seat of the the craft, and again know that there were supernatural powers at work, again revealing the existence of demons. Why not create a real life form, instead of a puppet? Because demon's do not have this power. Only God has this power. Only God can create life. Demons do make the aliens look alive though. When a person is abducted by "aliens" into one of their spaceships, they see "living" aliens. This is accomplished through a form of telekinesis, in which the demons use their supernatural powers to control all the muscles of the alien puppet, and thus make it look like it's alive. Why abduct anyone at all? Why go through the trouble of taking people on board a spacecraft, and probe them, and do science experiments on them, when demons have no need to do that? Well, that's part of the whole coverup the demons are doing. Remember, they are trying to make it look like space aliens are coming to the earth (and abductions and subjecting humans to experiments is one of the things people think about when they think about aliens), to hide the fact that it's really demons coming to the earth.
Ever wonder why the sight of space aliens often is so terrifying to people? They don't look that threatening, those little gray men. The fear is actually caused by an instinctive fear of dark/demonic supernatural forces that humans have. It is a very primal fear, and is built into us as a survival mechanism, because it is absolutely ESSENTIAL for us to NOT get involved with demons. While visually they don't look threatening, the evil magic energy field that surrounds a demon is detected by our human soul (our spiritual body) and sends a signal of fear to the emotional center of our brain, triggering a MASSIVE paralyzing fear response. Our body isn't sensing the presence of pure evil as that evil force is in a supernatural realm, and our body is in the physical realm, nor are our eyes seeing it, but we can tell that what is present in the room when aliens invade is more than we are seeing. We can literally detect the presence of an evil supernatural force in the room, through the senses of our soul (our spiritual body, rather than our physical body). And that soul interacts with our physical body (specifically the brain, which is the interface between our physical body in the physical realm, and our spiritual body in the spiritual realm), and this allows our brain and body in the physical realm to detect (and tremble in fear at) the presence of a nearby supernatural evil force in the spiritual realm.
If you see an "alien", NEVER just dismiss your fear as irrational. NEVER say to yourself "I shouldn't be scared, it doesn't even look scary. Why am I feeling so scared? That's just stupid.". If you see an "alien" RUN AWAY! Do NOT try to communicate with it. It is not a being from another planet. It is a puppet being controlled by a demon, and demons are angels who have rebelled against God. The occult is something you should ABSOLUTELY AVOID messing with.
No intelligent life from another planet would want to have anything to do with us humans. If they had the technology to fly thousands of light years to the earth, they would be so much more advanced than us that they would think of us no more interesting than ants, and not worth the effort to communicate with us. Furthermore they would see us as a violent species bent on killing each other, and they would not have any desire to get involved in such foolishness. Thus the demon theory of aliens is the only real explanation for all the "alien" and "UFO" sitings and abductions that have been reported.