In the sci-fi thriller film Skyline, Earth is invaded by an aggressive race of alien creatures. Next to nothing is known about these creatures, including the name of their race (if they have one). What is known is that they are bio-mechanical in nature and possess technology vastly superior to that of humanity. When they invade Earth, the aliens abduct the planet's population en masse and harvest the brains of their victims, planting them into alien bodies.
The aliens have a variety of different forms, each one designed for a certain purpose.
The alien drones resemble squids or octupi, having large ovoid bodies sporting multiple long tentacles. These creatures are capable of flying and act as the basic servant and soldier units of the alien invasion force, hunting down humans who have not been lured by the hypnotic field emitted by the alien motherships during initial contact. Drones seek out human stragglers to harvest their brains and will engage in combat with battle-ready humans. They also tend to the maintenance of the motherships; after one ship is heavily damaged by a tactical nuclear strike, it released a swarm of drones that went about regenerating the craft.
The Hydras are black flying aliens that function as dropships. They patrol regions being attacked and release drones to find prey. They have wings and one big blue eye. They are used as "suicide bombers" when combating enemy aircraft. They are also seen hunting down hiding humans.
Tankers are giant crab-frog like creatures with multiple eyes and 8 brains for "power". Instead of hypnotizing prey with blue lights, they have clingy tentacles which they use to hunt. They walk/run on four legs and are olive green in colour. They are incredibly strong and almost impossible to destroy but their skin is flammable and this capable of slowing them down. They are seen battling against groundside human soldiers and capture victims by releasing tentacles from orifices in their forelegs and pulling victims inside.
The purpose of this variation of the aliens is unclear. They could be workers, guards or soldiers. Their body structure is similar to a primate like a gorilla with long arms and short legs, so they move by dragging their knuckles. Every individual has multiple blue eyes and slimy, dark brown skin. Like the drones, they need a stolen brain in order to function. A Worker is seen inside a ripped-open drone towards the end of the movie, suggesting they may be the actual true species, who simply "pilot" the other lifeforms.