The Aliens are the main antagonists of the History Channel mockumentary When Aliens Attack, which is about what would happen if aliens invaded Earth.
Physiology
The Aliens are machines that come in five forms: robots, drones, harvesters, carriers, and the mothership. The robots are approximately three stories high and resembles a barrel on digitaroid legs. A green "eye" on the barrel serves as its main weapon, and it has a smaller gun below the "barrel." The drone is about the same size, but has wings instead of legs. The harvester is a roughly cylindrical craft ranging from 3-10 stories in height; the bottom is entirely occupied by a tractor beam. The carrier is a triangular craft perhaps half a mile across, and serves as a launch base for other aliens. The mothership is a 50+-mile sphere with several "fins" sticking out the back and a series of rods in a depression at the top. These rods serve as docks from which carriers are deployed.
Culture
From what is seen, Alien society is centered on the harvesting of chlorophyll and protein from planets. The Aliens are seemingly led by the Mothership.
Weapons
All Aliens, except for the carriers, are armed in some respect. The robot has a large "eye" that fires a green orb, most likely made of plasma, and has a small gun that fires a smaller plasma orb. The drone has a similar plasma cannon, but does not have a gun. The harvester uses its tractor beam to harvest plant and animal life, whereupon the chlorophyll and protein are extracted. The mothership has a massive EMP generator, and may have other weapons.
Diet
The Aliens are machines and do not feed. However, harvesters collect chlorophyll and protein as fuel for the Aliens, presumably using some for themselves and bringing it back to the carrier, which in turn uses some of that fuel for itself, distributes some more for the robots and drones, and finally takes the rest to the mothership when the invasion ends.
Homeworld
The homeworld of the aliens is unknown and abandoned. For all intents and purposes the mothership is their homeworld.