The aliens travel through space, visiting planets on which they project sort of blue energy that connect them all as lure which mesmerizes indigenous lifeforms. The victims are then harvested before their central nervous system is extracted to be used, it seems, as power source. The aliens are divided in several specialised subspecies, some of which have been witnessed.
The largest known entity is the Mother Ships which comes in all shapes and size but is usually several hundred meters long and able to travel interstellar distances, transporting the smaller specimens of the species. They seem to be moving in pack from worlds to worlds.
The Tankers are anthropomorph entities 20 to 30 meters tall. They are used as cleanup crew, gathering the indigenous specimens that have escaped being lured by the blue light.
The Hydras are the big flying squid creatures.
The drones are smaller octopus creature, which are able to enter tighter spaces.
There seems to also be smaller anthropomorph aliens which stays inside the mothersip and most likely others which have not been witnessed yet.