I like demons as they're portrayed in popular culture. I wanted to make a "anatomically correct" succubus question, but StackExchange tells me that this one already exists (even if it is not referenced in the anatomically correct series).

This answer and this one were pretty interesting, and inspired this question. I'm imagining a creature kind of like the Cymothoa exigua, but which turns the infected person into a succubus (or an incubus). For that, it would need to interact with its host to promote the growth of horns, wings, a tail, and a change to eye and skin color. Is this plausible in some way, or totally impossible?

  • $\begingroup$ Thanks for the note, I have added the Succubus question to the AC list in meta. $\endgroup$ – The Square-Cube Law Jan 17 '20 at 16:42
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    $\begingroup$ Why on Earth would a succubus have horns and a tail? Succubi are supposed to have the appearance of very attractive women. $\endgroup$ – AlexP Jan 17 '20 at 17:03
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    $\begingroup$ @AlexP in fairness, most depictions (nowadays) show a succubus as a very attractive woman...with prominent horns and tail. A lot of times wings as well. Because for some reason anything demonic has horns. And a tail. Most would have wings, too. Historically, a succubus might still have these but it's among other abnormal features. And it usually requires closer examination - at worse, a succubus might need to show up at night to make some marks harder to detect. But a lot of times, they'd be able to easily hide the deformity. $\endgroup$ – VLAZ Jan 17 '20 at 17:17
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    $\begingroup$ @AlexP most of the modern pictures of the succubus give them "demonic attributes" like horns, wings, tail, etc. And this is the kind of pictures that I have in mind. Plus, just if you see how much populars "demon-girls" tag is popular in porns and hentais websites, I think you can say that demon appearence don't make a succubus unattractive. $\endgroup$ – Rorp Jan 17 '20 at 17:43
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    $\begingroup$ @Astrid_Redfern eyes become blue (the entire eye, not just the iris), and the skin become pinkier $\endgroup$ – Rorp Jan 19 '20 at 7:27

Warning: I am going a bit into teratology here. If you google up the stuff I mention, you may find graphical things that can cause the most sensitive among us to lose a few nights worthy of sleep. I have abstained from providing links to those (otherwise what I'm linking to is sanity-safe). Look them up at your own caution.

Also: thanks to Astrid_Redfern for some extra info I have added to the post, regarding Shope papilloma virus and wing growth, eye and skin coloration, and behaviour effects of a certain parasite.

Is this plausible in some way, or totally impossible with rules of our world?

It is plausible. It is improbable that such a creature would would evolve in our world as it is now, but evolution might have gone differently.


Some people are born with tails. That's because some tail building genes are present in the human DNA, although deactivated. A mutation causes the genes to reactivate. Usually these people have their tails cut off shortly after birth. If we as adults were able to have more totipotent cells - that is, cells able to produce all kinds of differentiated cells - a tail could be grown after birth. The genetic activation might be provoked by a microorganism such as a virus, or a larger one like a worm could do it by injecting some hormones into the host.

An example of a parasite (in this case, a virus) causing something to grow in humans is epidermodysplasia verruciformis, a condition whose sufferers are called tree men. The growths are so huge that they frequently become larger than the person's fingers, rendering the hands useless.


Now I am quite sure we don't have the genes for horns (the horn in some cyclopic babies doesn't count as that is just flesh, also don't google it), though we do have the genes for increased amounts of keratin and bone, which is what horns are usually made of. For keratin, look at harlequin babies (warning, nightmare fuel). For bones, see osteochondroma.

Notice that leporids (bunnies and rabbits) are susceptible to infection from the Shope papilloma virus, which can lead to keratinous carcinomas (cancers) resembling horns. These usually grow on the head of the animal, in places where there is already hair growth. This could be your succubi/incubi horns right there, and might be the explanation of why the condition is unhealthy.


For this it might have to be a world where humans have some common ancestry with winged creatures. It's your world, and it's touching on the supernatural - you could justify it as people being descendants of angels, or true demons.

Alternatively (and perhaps more realistically), their wings might be like the leathery wings of a bat. A papilloma virus that makes the body produce just the right kind of skin might do the trick, connecting the wrist to the ankles. I believe such wings could even be functional - not for true flight, but for gliding. I have discussed this in another answer about human gliding, and also this one about human wings.


A bone condition known as osteogenesis imperfecta usually causes the cornea to have different pigmentation. This condition was made famous due to a trilogy of movies starring Bruce Willis (starting with one called Unbreakable). There is a picture of the effects on the eyes of a person in the wiki. It is one of the things in my list that is not disturbing, it just gives the cornea a different hue (though sometimes it also causes a slight eye protrusion). For the iris, some diseases such as Fuchs heterochromic iridocyclitis are known to cause discoloration. More causes for iris color changes can be found in the latter link.

Pigment dispersal syndrome can also cause eye color changes, with less short term adverse effects if you wish to tone those down. Long term it causes glaucoma and then blindness, though.

Something extra about eyes

It is said that people are seen as more beautiful when their pupils dilate. In the past people used belladonna (a poisonous plant) to achieve this effect, because humanity. In fact the name of the plant means "beautiful woman" in italian. I find it debatable whether stoned eyes are beautiful for today's standards, but if it beats their kink, it beats their kink.

Your succubi/incubi might have permanently dilated pupils. It will be seductive for some people, scary for others, and generally give them slightly better vision in low light or underwater.

Skin color

Trigger vitiligo for a paler skin. Or trigger porphyria, the vampire disease to make the afflicted so much sensitive to sunlight that they will get burns from levels of exposition that wouldn't tan healthy people. Avoiing the sun will make them paler. If you want people to be "pinker", rush blood to the skin. This might also cause their skin to feel warm to the touch.

Notice that all the conditions above are harmful and mostly unpleasant to the eye, but with the right evolutionary pressures you could have a more perfectly "demon" lookalike. If a succubus/incubus appearance causes the person to have more offspring, for example, evolution will push appearance that way. Why not everyone is a succubus, then, might be because either such people are killed due to superstition, or because the agent that causes such changes also causes a lot of harm in some other way. If all the agent did was beneficial to the host, it would be mutualism or commensalism, not parasitism.

Finally, succubi and incubi are known for either requiring sex to live, or to obtain strength. It might just be the stuff of legends, with the hormonal changes caused by the parasite resulting in a second puberty (except that now you are above legal age, so hooking up with people is easier).

Toxoplasma is a parasite of cats that is known to thrive in humans. There are many papers that say it affects human behaviour, and some that say it doesn't. Whether it is true or not in our world, it can be true in yours. Here is what a paper published Schizophrenia Bulletin of the Oxford University has to say about it:

Consistent and significant differences in Cattell's personality factors were found between Toxoplasma-infected and -uninfected subjects in 9 of 11 studies, and these differences were not the same for men and women. After using the Bonferroni correction for multiple tests, the personality of infected men showed lower superego strength (rule consciousness) and higher vigilance (factors G and L on Cattell's 16PF). Thus, the men were more likely to disregard rules and were more expedient, suspicious, jealous, and dogmatic. The personality of infected women, by contrast, showed higher warmth and higher superego strength (factors A and G on Cattell's 16PF), suggesting that they were more warm hearted, outgoing, conscientious, persistent, and moralistic. Both men and women had significantly higher apprehension (factor O) compared with the uninfected controls.

It is also known to drive testosterone levels up in male rodents. If a microbe is able to do that, it might also be able to drive a person's sex drive up given the necessary evolutionary pressures.

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    $\begingroup$ Renan and @Rorp - I'd like to suggest a couple of possible edits to this answer. First of all, there is a virus which causes horn-like keratin growths in rabbits, the Shope papilloma virus ( en.wikipedia.org/wiki/Shope_papilloma_virus). Although this virus typically affects the face and neck in rabbits, it targets "hair-bearing skin". For most women, this doesn't include the face and neck, so the virus would be most likely to cause these growths on top of the head - exactly where you'd expect horns to be. Secondly... see below: $\endgroup$ – Astrid_Redfern Jan 18 '20 at 22:30
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    $\begingroup$ @Astrid_Redfern thanks for the inputs, I'll edit to add those later on :) $\endgroup$ – The Square-Cube Law Jan 19 '20 at 2:24
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    $\begingroup$ @Astrid_Redfern I made an edit adding the info you provided. Thank you very much! $\endgroup$ – The Square-Cube Law Jan 21 '20 at 15:31
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    $\begingroup$ Nice one! But you might want to edit a little further - the Shope virus growths don't just resemble horns, they're made of the same stuff (keratin) so they should have the same properties as real horns. In fact, you could well argue that they are real horns. $\endgroup$ – Astrid_Redfern Jan 21 '20 at 19:50
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    $\begingroup$ Worth noting - belladonna wasn't ingested to cause pupil dilation, it was in eyedrops. $\endgroup$ – jdunlop Jan 22 '20 at 2:11

No, not if you want these structures to be functional and sexy.

There is a parasite that causes extra limbs to be produced.

A pacific chorus frog infected with  Ribeiroia ondatrae, National Geographic, 2010

A flatworm infects frogs and causes vestigial limbs to erupt at hideous angles so that the frog is eaten and the parasite can continue its life cycle.

This might seem promising for what you want to do, but there are some huge issues for your demon package.

  1. Developing functional horns, wings and a tail would require much more complex genetic alterations that the constant growth of legs.
  2. The legs on the infected frogs really don’t work because they aren’t properly supported with the muscle-skeletal structure like actual limbs, so good luck trying to fly.
  3. The point of these extra legs is to ensure the frog’s death and consumption, a succubus/incubus presumably wants to have sex, so extra limbs probably aren’t a good bet.

I have a different suggestion for a “Anatomically Correct” succubus that has a parasite origin. Have the parasite elicit no outward mutation on the human, but cause them to become so sexually obsessed that they are compelled to have sex and spread the infection. There are already diseases that effect the behaviors of the host.

One thing to keep in mind is that Incubi/Succubi were in their mythology originally rapists that had sexual contact with people while they slept, and were blamed for nightmares and wet dreams. So have your anatomically correct Succubi be a woman who has had all empathy and pity turned off and replaced with overwhelming lust due to the chemical influence of a blood parasite that spreads sexually.

  • $\begingroup$ Responding to points 2 and 3 - Richard Dawkins's "The Extended Phenotype" describes a parasitic fluke which infects snails. It increases the shell thickness of its host, improving survival fitness - hence "functional". It may also impair its host's reproductive fitness, but the evolutionary reasons for its doing this wouldn't apply here, since the succubus/incubus parasite relies on its host having sex to spread it. Do you think it might be worth editing your answer with this info? $\endgroup$ – Astrid_Redfern Jan 18 '20 at 22:46
  • $\begingroup$ As for affecting host behaviour - see my comment on Renan's answer. I've also posted about this on Biology.SE. $\endgroup$ – Astrid_Redfern Jan 18 '20 at 22:47

There are already quite a lot of parasites that toy with the reproductive behavior of the host. Toxoplasma gondii was already mentioned as one that controversially may cause this behavior in humans (and is known to warp reproductive behavior in other animals). Sacculina also messes with this, it parasitizes crabs and forces the host into a false pregnancy, making them perform the reproductive behaviors it normally would with its own eggs with the parasite. If it infects a male crab it turns them into a female and does the same thing, to the point that if the parasite is removed the male crab regenerates ovaries instead of testes.

The big question is what exactly is your parasite's life style. A lot of parasites sterilize their host once they establish their infection because if the host is engaging in costly reproducting behaviors (finding a mate, courting a mate, caring for offspring) they do so at their own expense and that is energy the parasite could use for its own purposes. But if the parasite is sexually transmitted, it's best bet for reproduction is to increase the host's sex drive to spread its offsrping everywhere but at the same time sterilize the host so it's not weighed down by caring for offspring.


Let's start in a biological warfare research laboratory where the absence of any evolutionary advantage to the parasite can be ignored in determining the fitness for survival of the trait-bearing offspring.

Introduced as a weapon targeted at distracting civilian populations, the parasite modifies the sweat glands of its host causing them to release airborne hallucinogenic pheromones. The illusion of horns, wings and tail are an unexpected side effect, possibly resulting from the Catholic school upbringing of the test subjects (and initial target populations). Overwhelmed by sexual urges brought on by the pheromones, the rational minds of the victims struggle for some explanation for their fall from puritanical grace. Hallucinating great beauty and demonic characteristics upon the target of their amorous affections help them feel more like demonic victims rather than horny sinners. Funny how the mind finds ways to justify whatever the body wants to do.

As the tales of demonic seduction propagate through the social networks of the targeted population, future victims become pre-programmed to hallucinate the same demonic characteristics as their predecessors. A cycle of reinforcing reports and new occurrences continues until the existence of the demons is accepted as scientific fact. At which point, every escape into debauchery will be blamed on demonic influence. The original parasite will no longer be needed as the target civilization spontaneously collapses into bacchanal.


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