What kind of a society would exist for an intelligent species that lays it's eggs/young in a host to gestate/grow? We have the spider wasps which paralyze their prey and lay eggs. While sometimes the host survives, most of the time it is eaten alive.

We have also have the botfly, which lay their eggs on a host, though generally not causing it severe harm.

And of course we all know about this

Alien bursting man's chest.

It seems to me that unless they can only use specific species to incubate their young like this, that they would tend to be a rather uncompassionate species to any outsiders. Seeing any animal large enough to be a potential host/meal for their young.

Adding more details for those who need them. In this case I was thinking they have reached as least the level of culture as Rome (any time in their 1000 year history).

The mobility of the host? I had nothing in mind, other than vaguely something like a sheep or deer up to an elephant.

How Precocious? I expect that when they emerge, they are at least as physically capable as say a fawn when born, maybe a little more. Mentally could be an infant working on instinct.

  • $\begingroup$ Could you be more specific about the behavior and capabilities of this parasitic species? I'm having a hard time coming up with an answer that doesn't involve several combinations of possible parasite-prey relationships. $\endgroup$
    – Green
    Mar 22, 2016 at 21:35
  • $\begingroup$ @Green I will try. Have any specific questions you'd like me to answer? $\endgroup$
    – bowlturner
    Mar 22, 2016 at 21:37
  • $\begingroup$ yes. I'm interested in the technological capabilities of the parasite, if any. Also, the mobility of prey species will greatly dictate how much effort a parasite parent can put into finding a newly hatched parasite. Also, I want to know how precocious the newly hatched parasites are. $\endgroup$
    – Green
    Mar 22, 2016 at 21:40
  • $\begingroup$ @Green added more. And I don't think it invalidates either of the other two answers. $\endgroup$
    – bowlturner
    Mar 23, 2016 at 1:59
  • 1
    $\begingroup$ The more you can say about this species' physiology or intended behaviour the better. If you're not confident tying behaviour to physiology, just specify whatever's more important to you, and I could extrapolate the one from the other. Is this a parallel Earth, or an alien world? Do they need to interact with humans, and if so, have they done so over a long period, or is this a first-contact scenario? I really like this sort of socio-biological question, and with some more details, I could elaborate on my answer even more. $\endgroup$
    – Monty Wild
    Mar 23, 2016 at 2:08

2 Answers 2


A parasitic lifeform cannot just extend its catalogue of potential hosts any time it likes. The initial movies in Ridley Scott's Alien series appeared to have a large plot hole that it is inconceivable that a naturally-evolved species could successfully parasitise not one but three completely alien species (Humans, dogs (in Alien3) and Predators (in Alien vs Predator)), but the revelation in Prometheus showed that these were engineered bioweapons, likely made for the specific purpose of eliminating mammalian life. The fact that they can also reproduce in the completely unrelated Predators, as well as grow in places where there are no practical organic resources other than air (containing carbon dioxide) and electrical power suggests that they are more likely nanotech than biological.

That said, if we had an evolved sentient species with a potentially-lethal-parasitic reproductive habit, it is more likely that the parasitic part of its life cycle could occur in a number of related species, since in evolutionary terms, to restrict the valid hosts to one species is to render the parasitic species vulnerable to the fate of their sole host species, and most species have related species that are also vulnerable to the same pathogens.

To use a real-world analogy, those host species might be able to be described as 'Homeothermic land-dwelling vertebrates above 25 kilograms body mass', or 'Squid and Octopi', or some other group of creatures that occur in the same biome as our parasitic species. Unless 'Humans' fall into the category of potential host species, even if they did not co-evolve, they would almost certainly be unsuitable as hosts. If by some coincidence humans resembled a valid, but totally alien, host species, implantation might be possible, but gestation would most likely be unsuccessful. The survival of the human in question, while likely but not assured, is probably much higher than that of the intended host organism.

Regardless of the nature of the potential host species, we must consider that obtaining a host is a reproductive necessity. By extension, we can reason that any successful parasitic species with any kind of mind at all, let alone extelligence (having a recorded culture) must develop an affection for its host species, and would most likely keep the host species around as pets, to be on-hand when it came time to reproduce. The hosts would be bred, pampered, nurtured - and then implanted, and nurtured some more, until their offspring killed the host, at which point the carcase would be devoured by the offspring.

Consider the effort and interest that humans put into reproduction. There would be no question of whether the members of the parasitic species kept host-pets, but how many and which species. If humans were obligate parasitic reproducers with other mammals, it'd be like asking, "Do you prefer dogs, cats, rabbits, sheep, goats,"... etcetera, and to receive a "I don't like pets at all" answer would be practically inconceivable, and would probably represent some sort of monastic, non-reproductive life-choice.

The species used as hosts would be selected to have traits that made them suitable as pets, including appropriate size and other traits that enhanced the survival of the parasitic species' offspring, as well as docility, up to and potentially beyond the point of implantation with the parasitic offspring. It would likely be far less risky to implant a pet than to try to implant a wild animal. It is likely that - if possible - the host-pets would be desensitised to the act of implantation by repeated instances of play-implantation. Species of host-pet that came to enjoy play-implantation would be highly prized.

While it is possible that the act of implanting the parasitic embryo - or even play-implantation - would be injurious to the host, in evolutionary terms, the longer the host survives post-implantation (until at or near birth of the parasitic offspring), the better, since we are talking about a parasitic species, not a sarcophagic species. Since in wild conditions, any injury can be fatal, from infection if nothing else, evolutionary pressure would be to minimise the trauma of implantation.

If humans were not on the list of the parasitic species' potential hosts (since, for example, they are from different worlds), then even if humans resembled a valid host, it is unlikely that they would be selected as a host, since the humans would most likely be seen as falling into the 'risky wild-animal-host' category.

If humans were not a typical host, but were a potentially valid host, it is still unlikely that a human might be selected as a host except by a thrill-seeking type of individual/couple who likes the thrill and danger of trying to implant wild - as opposed to domesticated - hosts.

If humans were amongst the list of valid hosts - which is unlikely given that human sentience enables us to realise that being a host is highly detrimental or even fatal - then human hosts would likely be kept as pets (or at best second-class citizens), and for the most part kept ignorant of their true purpose as hosts for as long as possible.

As for the parasitic species relationships with non-host species, there is no reason why we should assume that they might be any worse or more cruel from what they might be if the species in question were not parasitic reproducers. If we suppose for a moment that humans are parasitic reproducers with other mammals, that wouldn't change the way we relate to non-mammalian species, except perhaps in a positive way. Being biologically habituated to keeping pets (for reproduction) would tend to make keeping non-reproductive pets more likely. If humans kept other medium to large mammals around for reproductive reasons, we might still be more likely to like keeping birds or fish or small mammals than we already are as a non-parasitic species.

If our parasitic species did not see humans as a valid host, they would still be quite likely to be friendly, given their predisposition toward close association with other species (even if those other species are reproductive hosts). The potential problems might arise from the human side, as I can imagine that humans might be less than thrilled to find that a species that acts like Ridley Scott's Aliens to non-human species wants to be friends with them. As a case in point, Larry Niven's Pierson's Puppeteers are concerned that revelation of their reproductive biology (which is stated to be similar to that of a digger wasp, very similar to that in the question and this answer) to other species would lead to negative reactions towards themselves.

  • $\begingroup$ This is an awesome answer! $\endgroup$
    – bowlturner
    Mar 23, 2016 at 1:52
  • $\begingroup$ I was going to answer too but this pretty much covers it. Well said! $\endgroup$
    – Green
    Mar 23, 2016 at 12:41
  • $\begingroup$ Why so much focus on humans? I thought the question wanted to k ow more about the alien's culture, not about how they would think about humans. $\endgroup$ Mar 23, 2016 at 19:47
  • $\begingroup$ @XandarTheZenon, I was making a guess that bowlturner might be interested in the parasitic species' interactions with humans, especially since (s?)he posted a pic of an Alien chestburster. This was proven correct by bowlturner's response in comments to a question in my own comment. Even if no interaction with humans had ever been intended by bowlturner, the answer was still made more broadly applicable by including the sections on humans. $\endgroup$
    – Monty Wild
    Mar 23, 2016 at 22:13

That's a valid argument and it is certainly possible for an alien species to have that mindset. However he Xenomorphs were shown to care for their young and their eggs, so it's not the only argument.

Consider that most humans are at least partly carnivorous, we live by consuming other living things. Hatching our eggs inside them isn't really that big a departure. After all in theory we could see anything vaguely edible as potential food but dogs, horses, cats and much more for the most part go uneaten.

The key thing would be for these other species to achieve a mutually beneficial symbioses much as we have with the three species I list. By doing that both gain by working together and the urge to use Fluffy as an egg incubator is not actually a successful survival strategy when Fluffy can help you hunt down something else to do the job.


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