Original Psiren head from TV series Red Dwarf
Psirens are GELFs which can telepathically alter the perception of humans, in order to suck out their brains with a straw and take anything they can use. In their natural form, Psirens are insectoids standing at around two metres high and look something like giant beetles, with giant bulbous eyes and a large carapace. Their name and manner are similar to the Sirens of Greek mythology. They can't hide their true forms from electronic devices, only the perception of it from anyone seeing it (providing that they are in range of their abilities). They are also territorial and are willing to kill each other to feed on their victim's brains.
They do whatever is nessesary to lure their victims onto the asteroids, at first focusing their illusions on specific individuals. They also do this if they are alone, which is more successful as if in a group, the others are not as fooled by it.