The Xenomorph life cycle is quite complex. It basically boils down to this1:

  • Queen Xenomorph lays eggs.

  • Eggs hatch into facehuggers.

  • Facehuggers implant eggs in a host organism's throat.

  • Implanted eggs hatch into chest-bursters.

  • Chest-bursters grow into adult Xenomorphs. Their primary function appears to be serving the queen, protecting her eggs, and gathering host organisms and trapping them in the hive, where they can be easily implanted with facehugger eggs.

Although there are some parallels to real life social insect colonies, like ants, for example, this life cycle seems somewhat unique in that there are at least two different forms of life involved in the process: Facehuggers and Xenomorphs. If queens are distinct from other xenomorphs, that makes three different forms of life.

The most striking feature of the Xenomorph life cycle (and the part I am most interested in) is the facehugger: whereas most organisms go from being eggs to being babies/larvae to being adults, xenomorphs have a totally distinct sub-species, which is clearly not a Xenomorph itself, but is absolutely vital to the propagation of the species. That is to say, Facehuggers don't grow up, they don't turn into xenomorphs, and xenomorphs don't turn into Facehuggers, but you can't get a Xenomorph without first having a facehugger.

By way of comparison, a parasitoid wasp is always a wasp. The adult lays eggs in a host organism, the eggs hatch into larvae, the larvae metamorphosize into adult wasps, and so on. But xenomorph queens lay facehugger eggs, and Facehuggers lay Xenomorph eggs. Facehuggers don't resemble xenomorphs in any way, and vice versa. Xenomorph queens can't lay Xenomorph eggs. Only Facehuggers can do that. Facehuggers can't lay facehugger eggs. Only Xenomorph queens can do that.

Did Ridley Scott model the Xenomorph life cycle after a real world species, or did he just make the whole thing up himself?

1 I know that the director's cut of the first Alien movie shows people being turned into eggs, but I decided not to mention it because it would only muddy the waters without substantially changing the thrust of the question.

  • 9
    How about this? Alternation of Generation and Exceptions in Cnidaria--"Alternation of generations is a type of life cycle that switches between two forms, the asexual polyp and the sexual medusa. Each reproduction, one form will give rise to the other. For example, a polyp will go through asexual reproduction to produce medusae and vice versa with sexual reproduction among medusae." I don't know of any evidence that Ridley Scott or any of the Alien script writers were inspired by this particular organism though.
    – Hypnosifl
    Commented Aug 3, 2015 at 19:30
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    @Hypnosifl - I'd upvote that if you made it an answer.
    – Wad Cheber
    Commented Aug 3, 2015 at 19:35
  • 6
    Have you considered that the facehugger doesn't insert an egg, but actually inserts itself and leaving the outer (face hugging) shell of the creature?
    – Pieter B
    Commented Aug 4, 2015 at 10:53
  • 2
    A somewhat missed point that doesn't allow Cnidaria and flukes as perfect comparisons, is that they don't discard what seems to be a perfectly complete and living individual to die while proceeding with their life cycle. It's as though molting involved not just a new outer layer, but a new set of organs, parts of the brain included.
    – kaay
    Commented Aug 4, 2015 at 14:15
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    I think it is worth mentioning that, despite the non-muddying of waters, the egg itself appears to be some form of autonomous creature (i.e. it opens itself, not by the influence of the facehugger within etc). As for the classes of creature which do this on earth, then caterpillars to butterflies?...
    – Paul
    Commented Aug 4, 2015 at 16:24

7 Answers 7


TL;DR: Not entirely. The Xenomorph lifecycle appears to be a mash-up of several actual lifecycles - mostly insects & parasites, yet isn't 100% identical to any particular one.

Writer Dan O'Bannon's original lifecycle was based on a variety of different insects, and was also very similar to parasites like M. ancylivorus.

  1. Adult lays the egg on a host
  2. Egg hatches the parasitic larva, which burrows into the host
  3. Larva uses host to gestate & form cocoon
  4. Juvenile version of adult insect hatches from cocoon

This is nearly identical to O'Bannon's original Xenomorph lifecycle:

  1. Adult creates the egg
  2. Egg hatches the face-hugger, which finds a host & implants embryo
  3. Embryo uses host to gestate & grow
  4. Juvenile version of adult Xenomorph hatches from host

In fact, O'Bannon has said that parasitic insects were his primary inspiration:

When Dan O’Bannon started conceptualising his alien creature he turned to two key influences: the creatures depicted in the comic books he devoured as a child, and the insect world. “Works of fiction weren’t my only sources,” he explained in his essay Something Perfectly Disgusting. “I also patterned the Alien’s life cycle on real-life parasites … Parasitic wasps treat caterpillars in an altogether revolting manner, the study of which I commend to anyone who is tired of having good dreams.”...

and director Ridley Scott has also quoted insects as the inspiration behind the creature:

In the 1999 DVD commentary, Ridley Scott explains: “The whole notion of this [creature] was taken off a certain kind of insect that will find a host, lay its eggs, and then in that host it will bury its eggs, and then of course the eggs will grow and consume the host. So that’s the logic of it all. Probably what makes a lot of nature go around.”

Note that the extra "phase" of the Alien Queen was introduced in the sequel, with which O'Bannon had no involvement. James Cameron felt that Ripley needed an "equal" to face in the film's climax, and subsequently designed the giant Queen to fit that need. The Queen concept does, however, stick with the same insect motif.

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    There is a slight difference in that the larva goes into a cocoon where its body is modified but it doesn't actually reproduce, whereas the facehugger seemed to lay an egg or larva which was a separate organism from itself.
    – Hypnosifl
    Commented Aug 3, 2015 at 20:50
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    But your example doesn't seem to include an intermediate stage represented by a distinct form of the species. The facehugger is the real anomaly here - they represent an intermediate stage, and I am not aware of any evidence that Facehuggers ever become anything other than Facehuggers. Aside from laying Xenomorph eggs, they have nothing in common with xenomorphs. They don't turn into xenomorphs, and xenomorphs don't turn into them. This is the bit that really puzzles me
    – Wad Cheber
    Commented Aug 3, 2015 at 21:10
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    Given that the facehugger dies immediately after laying the embryo, I don't think it's a separate organism. It instead seems to be the transportation method of the larval stage. You could argue that the facehugger organism is what's being deposited, and the facehugger as we know it is just a shell that falls off afterwards.
    – Omegacron
    Commented Aug 3, 2015 at 21:29
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    Considering that the xenomorphs take on certain aspects of their hosts (case in point, the dog xenomorph), it could be that the queen is simply the result of infecting a social organism with a queen/worker stucture. A trait which was then incorporated into all subsequent xenomorphs in that line.
    – Peter
    Commented Aug 4, 2015 at 21:13
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    @Omegacron: good point, and one could perhaps draw a loose analogy with a retrovirus. The viral body is the facehugger, the RNA is the egg that the facehugger lays. The DNA provirus represents the burster/xenomorph/queen, but it never actually "bursts". At this point the analogy doesn't quite hold, since the queen lays eggs that hatch into facehuggers, whereas the provirus generates viruses directly. I doubt that this inspired Alien, but it's an example of a substantial body whose "purpose" is transport and that is discarded once that's accomplished. Commented Aug 5, 2015 at 13:14

Life cycle that may have influenced that of the Xenomorph

It has recently been suggested that Phronima was the inspiration behind the Xenomorph:

enter image description here

From the Wikipedia article concerning Phronima:

Although commonly known as parasites, they are more technically correctly called parasitoids. Instead of constantly feeding on a live host, females attack salps, using their mouths and claws to eat the animal and hollow out its gelatinous shell. Phronima females then enter the barrel and lay their eggs inside, and then propels the barrel through the water as the larvae develop...

If  the articles above are correct and Phronima is indeed the inspiration behind the Xenomorph, then it is easy to see how one might extrapolate the Xenomorph's life cycle from Phronima's.

Life cycle that is more like that of the Xenomorph

However, Phronima's life cycle is not exactly that of the Xenomorph. For an animal using intermediate offspring to reproduce, I would nominate Cnidaria, which @Hypnosifl has already mentioned prior to my answer. Cnidaria includes jellyfish and the common sea nettle. A group of the latter is pictured below:

enter image description here

Here is a pictorial representation of their life cycle:

enter image description here

Steps 4-8 show the growth and release of the "polyp", an intermedia offspring which will give rise to the "medusa", which is the full animal.

In regards to plant species, ferns are a good example of a plant that uses an intermediate offspring to reproduce.

Another interesting Alien-esque life cycle in nature

May I present to you Dicrocoelium Dentriticum, better known as the Lancet Liver Fluke, a.k.a. "Captain Higgins" :

enter image description here

  • Its eggs are defecated by a cow or horse, etc.
  • The eggs are eaten by snails, in which they hatch into larvae
  • The larvae mature to juvenile stage within the snail
  • As a reaction, the snail grows a cyst to surround the juveniles, and then the parasite-filled cyst is ejected by the snail
  • The juvenile flukes are once again in an egg, but they used the snail to create it for them
  • The cyst-egg is consumed by an ant, after which it breaks open
  • The juveniles flow and/or burrow up to the ant's brain and latch onto it causing the ant to climb a blade of grass each evening until the blade of grass (and the ant and the juvenile flukes) are consumed by a cow or horse
  • Inside the cow or horse, they mature into adults and lay eggs
  • Poo, repeat

enter image description here

Again, not quite the life cycle of the Xenomorph, but there is a two-stage process here that involves at least three animals being seeded along the way.


Various life cycles in nature — e.g. Phronima, Cnidaria, Ferns, Lancet Liver Flukes — have features in common with that of the Xenomorph. However, the facehugger, which is a wholly separate lifeform that lays its own egg via a proboscis into a host, seems to be unique to the Xenomorph. I can find no evidence for it in the "real world".

In a sense, the thing that comes closest is common bisexual animal reproduction. The only caveat is that sperm don't lay their own eggs!

  • 5
    You deserve a bounty for mentioning Captain Higgins. Great answer, and a million thanks. I still don't see evidence of a distinct intermediate stage, which has no relation to the other stages (aside from laying the eggs). Both of these examples show one organism going through a series of changes, but Facehuggers don't change into anything else. I am beginning to suspect that the facehugger phenomenon is unique, and has no parallel in the real world.
    – Wad Cheber
    Commented Aug 3, 2015 at 22:42
  • @WadCheber : Thanks! I would tend to agree with you: while parts of the Xenomorph life cycle may be inspired by various oddities of nature, I suspect that the facehugger is indeed unique.
    – Praxis
    Commented Aug 3, 2015 at 22:47
  • I couldn't resist the temptation to insert a link to The Oatmeal's cartoon about Captain Higgins. Hope you don't mind. :)
    – Wad Cheber
    Commented Aug 4, 2015 at 1:14
  • @WadCheber : I approve. ;-)
    – Praxis
    Commented Aug 4, 2015 at 5:09
  • 2
    +1 Great answer, but you neglected to mention that the liver fluke is telepathic, highly intelligent, and excels at advanced mathematics.
    – user14111
    Commented Aug 4, 2015 at 8:22

There is a real phenomenon like this in some species known as "alternation of generations", where an organism with body type A will have an organism with very different body type B as an offspring, and then the organism with body type B will have another one with type A as an offspring. An example is discussed on the page Alternation of Generation and Exceptions in Cnidaria, which says:

Alternation of generations is a type of life cycle that switches between two forms, the asexual polyp and the sexual medusa. Each reproduction, one form will give rise to the other. For example, a polyp will go through asexual reproduction to produce medusae and vice versa with sexual reproduction among medusae.

I don't know of any evidence that Ridley Scott or any of the screenwriters were inspired by real-life examples of alternation of generations, though.


I think I found the answer myself. As has been suggested, the Xenomorph life cycle is loosely based on the life cycles of parasitoid insects.

From the excellent site Strange Shapes ("Strange Shape" is the literal translation of the word "Xenomorph"):

The Inspiration for the Xenomorph:

Facehugger and Chestburster

When Dan O’Bannon started conceptualising his alien creature he turned to two key influences: the creatures depicted in the comic books he devoured as a child, and the insect world. “Works of fiction weren’t my only sources,” he explained in his essay Something Perfectly Disgusting. “I also patterned the Alien’s life cycle on real-life parasites … Parasitic wasps treat caterpillars in an altogether revolting manner, the study of which I commend to anyone who is tired of having good dreams.”...

The insect world, O’Bannon knew, was one of sheer brutality, where even acts of copulation routinely result in murder. ...Insects are also notoriously cruel to other species of insect – the relationship between flies and spiders is an obvious horror, but varieties of wasp also use the bodies of other insects as the host for their young. A genus of the Phoridae fly, the Pseudacteon, also known as the ant decapitating fly, is infamous for its violent use of ant bodies: eggs are laid in the ant’s thorax, and the larvae migrates to the brain, where it feeds on the hemolymph and muscle and nerve tissue. “After about two to four weeks, they cause the ant’s head to fall off by releasing an enzyme that dissolves the membrane attaching the ant’s head to its body. The fly pupates in the detached head capsule, requiring a further two weeks before emerging.”

"It was our idea,” explained Ron Shusett to Cinefantastique, “that it would be the life-cycle of an insect. The way a wasp will sting a spider, paralyze it, and lay its eggs in the spider. Its eggs grow off the living spider, like a surrogate mother. That we did want it to be.”

Ridley Scott added: “There’s a fundamental connection in nature because we actually watched, in preparation for this [movie], Oxford Scientific, [which] had this interesting piece of footage where they’d watched a slice of bark, and there’s a grub underneath the bark … Across the top of the bark was this insect, which passes over the grub, stops, backs up, and ‘feels’ the grub is there, let’s say, the equivalent of 8 feet below you. It goes up on its hind legs, produces a needle from between its legs, and drills through the bark and bulls-eyes right into the grub and lays its seed, so that the grub becomes the host of the insect.”

At first, O’Bannon was stuck on the point of getting the Alien on board the spaceship. Having it simply sneak aboard seemed too banal. But if the creature could stow away within the body of a space-man… Dan, fascinated and repulsed by the horrific life cycle of parasitoid wasps, incorporated the concept into his alien monster. It would gestate inside a living host and explode from their body. The Alien could get on the ship, and excitingly, not without spilling blood.


What gave us the cocoon concept was that insects utilise others’ bodies to be the hosts of their eggs,” Ridley said in 1984. “That’s how the Alien would use Dallas and each of the crew members it kills. This explains why the Alien doesn’t kill everybody at once, but rather kills them off one by one: it wants to use each person as a separate host each time it has new eggs.

Insect Features of the Xenomorph:

The Insect Influence

“The Alien franchise bases its Xenomorph life cycle on parasitic wasps on Earth,” Terry Johnson, a bio-engineering researcher at the University of California, told Popular Mechanics. “It’s a pleasure to see a film that acknowledges just how weird life can be.” But despite the blatant insectile nature of the Alien (specifically its four-staged life cycle and cocooning) and despite O’Bannon, Ron Cobb, Ron Shusett, HR Giger, and Ridley Scott being clear on the issue, fans have been reluctant to admit the insect influence on the original creature, instead brushing it off as an addition made by James Cameron in the 1986 sequel. However, in light of the evidence pointing to the original Alien makers being heavily and happily influenced by insects, attributing this to Cameron is akin to blaming wet streets for rain.

The connection between the Alien and insect reproductive cycles was so crucial that O’Bannon identified it as of “core psychological significance” before quoting biology and science journalist Carl Zimmer: “when an alien bursts out of a movie actor’s chest … it is nature itself that is bursting through, and it terrifies us.”

“I modelled [the Alien] after microscopic parasites that moved from one animal to the next and have complex life-cycles,” Dan explained. “I just enlarged the parasite. I was interested in the biology of aliens, so I wasn’t interested in streamlining the thing below interest level just for the sake of economy.” Ron Shusett, Alien‘s executive producer and friend to O’Bannon, told Cinefantastique: “It was our idea that it would be the life cycle of an insect. The way a wasp will sting a spider, paralyse it, and lay its eggs in the spider … that we did want it to be …. We thought people might pick up on it and say, ‘yeah, an alien life cycle can be an insect life cycle.'”

Alien and Aliens conceptual artist Ron Cobb further explained the origins of the chestburster scene: “He got that from the paralysing wasp … it paralyses the spider and lays its eggs on the spider, then buries it in the ground so that the living spider serves as food for the wasp larva and you know, he always was so horrified at that idea.”

In the 1999 DVD commentary, Ridley Scott explains: “The whole notion of this [creature] was taken off a certain kind of insect that will find a host, lay its eggs, and then in that host it will bury its eggs, and then of course the eggs will grow and consume the host. So that’s the logic of it all. Probably what makes a lot of nature go around.”

I wanted him [the Alien] to be insect-like. Like an ant. Because if you examine an ant under a microscope they’re kind of elegant, and I wanted him to be very elegant and dangerous.” - Ridley Scott, The Alien Saga, 2002 (archival interview from 1991)

“We decided to make a very elegant creature: quick, and like an insect.” - HR Giger, Cinefex, 1979.

enter image description here

Egg silo by HR Giger, embedded into the underbelly of the derelict spacecraft like, in Giger’s words, a termite nest. Originally, the eggs were to be housed inside a pyramid structure, but budget and time forced the filmmakers to economise. “[W]e had to combine the derelict ship and the hatchery silo,” said Giger. “I thought we could place the egg silo under the ship, a bit like termites do.” He concluded, “we decided it would be a good idea to have these eggs inside the derelict like termites inside the walls of a house.” Image copyright HR Giger.

To sum up the insectile traits of the Alien:

-The parasitic life cycle: The Alien is a parasitoid, needing a host in order to reproduce, like parasitic wasps. Ron Cobb identified the paralysing wasp as influencing O’Bannon. These wasps paralyse potential hosts and implant their seed along with a virus that suppresses the immune system which allows the larvae to grow undetected by the host. The large, formidable looking ovipositor of the Ichneumon wasp is not used to sting and wound, but to sting and impregnate.

The Alien can be more accurately described as a protolean being, defined by Wikipedia as creatures “that begin the growing phase of their lives as parasites, and in particular, typically as internal parasites. As a rule they end that phase of their lives parasitoidally by killing or consuming the host, and then they emerge as free-living adults.”

-Larval, pupal, and adult life-stages: From the egg comes the facehugger, the first stage of the Alien life-cycle. The facehugger’s function is to locate, subdue, and impregnate a host via its proboscis. The impregnated host is the pupae stage. Once the Alien violently emerges from the host it must shed its skin and grow in order to become an adult. Butterflies go through a growing process known as Complete Metamorphosis – meaning its adult stage is completely different to its larval stage, as is the adult Alien from its infanthood as a chestburster. Once the chestburster has shed its skin (as most insects do, usually shedding exoskeletons numerously into adulthood) it leaves behind the instar stage of its life and becomes an adult.

-Cocooning: The Cicada Killer Wasp cocoons its prey near the eggs of its young so that the newly hatched wasps have a food source. In Alien, the Alien cocoons Dallas and Brett not to feed on them, but for reproduction (though in early scripts, the Alien did eat parts of its cocooned hosts – it even ate Lambert whole in one version.) In Aliens, the colonists are abducted, subdued, and embedded into the walls of the hive to await death. In scripted, but unfilmed, portions of Alien 3, the prisoners were to come across the Alien’s nest, where they discover a cocooned Superintendent Andrews along with other half-eaten bodies. The characters identify the nest as a “meat locker”, presumably where the Alien stores hosts and food for its inbound Queen.

All of these elements bar the cocooning were present in the theatrical release of Alien. We see the Alien progress through the various stages of its life, getting a glimpse of some shedded skin along the way and even hints of the creature’s limited lifespan – “I wanted a sense of a timeless, slightly decaying creature that, maybe, only has a limited life cycle of, maybe, four days like an insect,” said Ridley Scott, adding: “the Alien lifeform lived to reproduce … [Ripley] killed it, but it would have died soon anyway. It’s like a butterfly.”

Insectile additions to the Alien life-cycle in the sequel:

-The hive: like ants and most wasps (not all are eusocial), the Aliens adopt a functionalist, hierarchical social system. Contrary to popular belief, this does not consist of drones and warriors. Cameron scripted Alien drones in his 1983 treatment but cut them in the next draft. When JamesCameronOnline asked John Rosengrant if the drones even reached any preliminary design stages, he answered: “Not really, as far as I remember.” Cameron himself explained that the term ‘Alien Warrior’ was not to denote two different kinds of Alien (as is often mistaken) but was merely “my term for the single adult seen in Alien.” The expanded universe and fanon generated the idea that domed and ribbed head Aliens represent two different castes, but this has no basis in the release version of Aliens and perhaps belongs and owes its popularisation more to the comic books and games.

-The Alien Queen: The Alien society within the hive consists of adult Aliens and their mother, the Queen. Unlike ants or termites, the Alien Queen does not have a need for a male counterpart (ants employ drones, and termites have kings to impregnate the queen). Like the creature in Alien, the Queen is ambi-sextrous, a hermaphrodite, capable of reproducing without the seed of a male. “There are insects like that [androgynous, asexual]” Ridley Scott said of his Alien, “so we based that on a little bit of good old Mother Nature.” The original creature was at first envisioned as a female, before becoming thought of as a hermaphrodite by Scott once Bolaji Badejo was cast (initial efforts to cast a tall, thin woman failed). The Queen likely carries a feminine title (just as the first Alien was dubbed “Kane’s Son”) for clarity and because we tend to struggle without gender-specific labels (though it should be noted that Cameron referred to the Aliens in a male/female capacity – though he also noted that they can change gender if a Queen is present or absent).

It’s usually thought that the insect elements began and ended with Cameron, but in fact not only did they begin with Dan O’Bannon, but they were continued and pursued even by David Fincher for Alien 3.

From the fears and morbid interests of Dan O’Bannon, through Ridley Scott’s research into insects, and Ron Shusset’s declaration that an insect life-cycle was the intention, it cannot be denied that the Alien is an amalgamation of horrific insectoid sexual aesthetics and traits, which contributed not only to the nightmare inducing nature of the creature, be its abilities, its visage, its growth cycle, but to its integrity as a space dwelling avatar of death as well. Strip the monster of all insectile traits and nothing reminiscent of the series’ Alien is left. Alien, Aliens, and Alien 3 managed to equilibrate the sexual and insectile overtones to create a startling, original beast, an equilibrium upset in the expanded universe and spin-offs, which saw a dilution of the creature’s sexual elements and subsequent diminishing returns.


The Xenomorph was modeled after a number of different species of insects. The life cycle was inspired by parasitoid insects, especially wasps. The Xenomorph's appearance, behavior, and anatomy were partially inspired by ants. The facehugger eggs were modeled after termite eggs.


From another angle, such an organism is biologically possible. And I'm talking about the acid blood here.

Just think that instead of carbon-oxigen based, the life form is silicon-sulfur based. For such a species, methane derivatives could be a sustainable atmosphere. CH4 or a similar thing could be for Si-S organisms like O2 for C-O organisms. H2SO4 would be the blood and the organism would require CH4 or derivatives and act similar to a methane to methanol reaction. This is a most complex discussion for another topic, but I'm just saying that it is arrogance to assume that all life requires oxigen and water as primary elements.

Getting back to the Xenomorph many-step evolution, it is under this form because the adaptability requirements (considering all: environment, meatbags possible to be used for breeding and hostile species. This is also confirmed by the later movie where the queen evolves to give birth directly to a live specimen. That in theory is an evolution by in practice it could fail to be sustainable in the many of the environments where xenomorphs live in. A living spawnling will be unable to stand-by until proper conditions are met for it to have all the necessary resources to survive. From this p.o.v. the egg-FH-microegg-minixeno line has better survival chances. How you followed the logic here.


So ferns do this. The adult fern will grow from a fully fertilized alternate version of the plant called a gametophyte. Gametophytes carry both male and female reproductive elements, but are not technically seeds.

The xenomorph is a fully fertilized and grown "fern/sporophyte" where the egg/facehugger is a "gametophyte". My guess is that the species, instead of carrying male and female reproductive elements in facehugger form, carries a blank slate embryo that needs additional DNA to become fully fertilized, hence the adaptability and fully plastic body type of the different genres of xenos.

  • 1
    I can see that the two are similar, but is there any proof (i.e. word of god) that Xenomorphs were based on ferns? Commented May 21, 2017 at 14:56

As a slight alternative point here: my understanding is that the original design of the Xenomorph had it have a phallus come out of its mouth in place of the inner jaws. It would impregnate the host orally. The decision to change this was for a variety of reasons, many of which should be fairly obvious (studios...).

So, if we go off of the original design, then yes there are a number of species which inject fertilized eggs into a host who erupt on birth.

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