Ayliens are a powerful, dangerous extraterrestrial species. While they are not known to be native to Sluggy Prime, they have appeared in various other dimensions where they have been called various other names: in the Dimension of science fiction cliches, where they are called Xenomorphs; and in the Dimension of Ghouls, where they are called Ghouls.
Ayliens are natural shapeshifters, taking on different forms to adapt to their environment. As such, their appearance and abilities can vary greatly from individual to individual. However, their species can be divided into two major categories: Drones and Hive Kings/Queens.
The majority of Ayliens are drones. When young, they undergo many rapid metamorphoses to adapt to the conditions of their environment. As they grow older, these metamorphoses begin to require spending increasingly lengthy periods of time inside cocoons.
A drone which adapts to gain higher intelligence has the potential to become a Hive King or Hive Queen.
A Hive King or Queen is capable of asexually producing drone offspring, passing on to them the adaptations that it acquired during its own time as a drone. Hive Kings/Queens are also capable of prolonging their vitality far beyond the normal lifespan of a drone by consuming the life-energy of the drones that they spawn.
Once the planet on which a Hive King or Queen resides has been rendered bare of all life, it sinks deep into the planet's core and destroys it from within. Fragments of the planet carry hibernating drones through space, carrying them to new worlds where some will become new Hive Kings and Queens, continuing the Aylien life-cycle.