Alien (When Aliens Attack)

These aliens are a mysterious species which invaded Earth in the early 21st century.

Biology
The aliens that invaded Earth are a race of machines, presumably created by another civilization and sent out to find planets where organic life exists and harvest that life to be used as fuel.

These machines come in five forms: Robots, Drones, Harvesters, Carriers, and the Mothership. The Robots are approximately three stories high and resemble a barrel on digitigrade legs. A green "eye" on the barrel serves as its main weapon, although it also has a smaller gun below the "barrel". The Drone is about the same size, but instead of legs, it has wings shaped like scythe blades. The Harvester is a roughly cylindrical craft ranging from 3-10 stories in height, its bottom 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 an approximately 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.

Diet
The aliens are machines and do not feed. However, Harvesters collect chlorophyll and protein as fuel, presumably using some for themselves and bringing the rest back to the Carriers. They in turn consume some of that fuel and distribute some more for the Robots and Drones, and finally take the rest to 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.

Abilities
All of the alien machines are extremely durable and/or agile. A Drone was able to effortlessly dodge missiles from a pair of F-18's before destroying the planes with similar ease, and the Carrier above Washington D.C. survived unscathed after being hit by eight nuclear warheads with a total strength of 1.5 megatons (which is because it spends extended periods in space being battered by space dust and cosmic rays). The only external weapon shown to harm an alien was a rail gun used to shoot a Robot at a range of 100-200 feet. They are, however, much weaker on the inside, as a primary tactic of the Human rebels was to "feed" the Harvesters bombs. Even the Carriers are vulnerable in this regard, as several strategically placed bombs were able to cripple them.

Culture and society
From what is known, the aliens' society is centered on the harvesting of chlorophyll and protein from planets in which carbon-based life exists. The invading forces are led by the Mothership, which might take orders from the aliens' distant homeworld, assuming that they even have one.

Appearances

 * National Geographic documentary, When Aliens Attack (2011)