Someone who can't die? That sounds like the definition of a zombie. Now for the aliens lets take a look at the whole passage, and not use any real commentary:
The fifth angel sounded his trumpet, and I saw a star that had fallen from the sky to the earth. The star was given the key to the shaft of the Abyss. 2 When he opened the Abyss, smoke rose from it like the smoke from a gigantic furnace. The sun and sky were darkened by the smoke from the Abyss. 3 And out of the smoke locusts came down on the earth and were given power like that of scorpions of the earth. 4 They were told not to harm the grass of the earth or any plant or tree, but only those people who did not have the seal of God on their foreheads. 5 They were not allowed to kill them but only to torture them for five months. And the agony they suffered was like that of the sting of a scorpion when it strikes. 6 During those days people will seek death but will not find it; they will long to die, but death will elude them.
7 The locusts looked like horses prepared for battle. On their heads they wore something like crowns of gold, and their faces resembled human faces. 8 Their hair was like women’s hair, and their teeth were like lions’ teeth. 9 They had breastplates like breastplates of iron, and the sound of their wings was like the thundering of many horses and chariots rushing into battle. 10 They had tails with stingers, like scorpions, and in their tails they had power to torment people for five months. 11 They had as king over them the angel of the Abyss, whose name in Hebrew is Abaddon and in Greek is Apollyon (that is, Destroyer).
It says they came down to earth, so that means they're somewhere from outer space. They had human faces, but the body of a horse? Then it says the sound of their wings was like the thundering of many horses and chariots rushing into battle. My guess is these scorpion horses were riding around in helicopters during the vision. Since he saw them inside the helicopter he assumed the whole helicopter was apart of their body, but thats what came to mind when it said the wings sounded like thundering of many horses and chariots rushing into battle.
Thats my random thought for the day.. What do you guys think?