“I’m sure someone’ll correct you in the comments”

You better believe it. Me and my 1st edition Space Hulk mission/background book are here to save the day.

“Genestealers reproduce by a method which is vastly different from humans. There are no ‘male’ or ‘female’ Stealers; Stealers are incapable of mating with each other, and they are unable to bear their own young. Stealers reproduce by infectiong other races with their genetic material.

Stealers are strong psychics. They are able to paralyze their victims with their gaze, in much the same way snakes terrify their prey into immobility. If a stealer concentrates all of his energies upon dominating its victim, only the strongest willed can resist. Once a victim is dominated the Stealer infects him, passing on its genetic material in an obscene parody of a kiss.

The Genestealers’ long supple tongues are equipped with ovipositors (egg layers). When a Stealer ‘kisses’ a victim, the tongue pierces the skin, leaving an egg behind. After a victim is infected he is released. Whether as a by-product of the Stealer’s hypnotic gaze or as a result of the hormonal secretions of the egg itself, the victim has no memory of the implantation, he sees the entire episode as a nightmare of fear, and burning eyes.

A subtle psychic link is established between the Stealer and its victim. The Stealer can influence the victims’ thoughts and actions without the victim realizing that he is being manipulated. The Stealer uses this power to give its victim one overwhelming desire; to mate and have children.

Because of the damage to the victims genetic structure, though he mates with his own kind, his children will be hybrids, part victim race, part Genestealer. Until the fourth generation, the hybrids are sterile, able to procreate only via the Genestealer method.”

Where Geiger’s Aliens preyed on certain primal fears, such as rape anxiety and parasite infestation, I think the Genestealers are even more brilliantly well-thought out as a horrible alien menace. The Genestealer’s embrace is more of a violation than that of the Aliens, because the kiss is typically thought of as being more tender and intimate than an anonymous impregnation, and here it is turned on its head and becomes an essentially violent act.

Where Geiger’s Aliens were designed to appeal to feminine fears, the Stealers are made to be threatening to men. They’re scary because they make their victims less masculine, paraliyzing them with fear, forcing them to “receive” the Stealers’ act of reproduction, invading and infesting the planet (the territory) the man is duty-bound to protect for his own peoples’ life and well-being; and cuckolding them by forcing them to produce, and to spend the rest of their lives raising and providing for, the Genestealer’s progeny rather than their own.