The succubi are popularly represented as women with horns and bat-like wings. They feed on the vital energy in myths, but could a humanoid creature resembling a woman evolve and feed only on human sperm? If so, what kind of animal and environment could trigger the evolution of succubi?

Note : These succubi don't really need to evolve horns and wings, just feed on human sperm and resemble a woman. They don't need to be attractive to humans. They just need an humanoid shape of any size with feminine traits and a predatory behaviour to ambush their prey.

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    $\begingroup$ The word succubus is a good word, describing a well-know fantastic being. They do not "feed on vital energy", and while they might have horns or wings, they most certainly don't appear to. They absolutely do appear attractive to men. Whatever it may be, this bizarre semen-eating being is not a succubus. $\endgroup$ – AlexP Aug 9 '18 at 5:49
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    $\begingroup$ @AlexP, the succubus I am aware of feed on male semen, and causes night pollution in men to get their food by appearing like women in their dream. $\endgroup$ – L.Dutch - Reinstate Monica Aug 9 '18 at 8:04
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    $\begingroup$ @L.Dutch: A standard succubus is a female demon who appears in men's dreams and seduces them. (The corresponding male demon is an incubus.) Their seductiveness is an essential aspect. As supernatural beings they do not feed on sublunar substances such as semen. $\endgroup$ – AlexP Aug 9 '18 at 8:08
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    $\begingroup$ 1) Succubi don't "feed" on semen. They collect the semen, switch their form to incubus and use it for impregnating women. Rationale is to work around a limitation of ungodly creatures being incapable of an Act of Creation. Succubi/incubi could be eating at your local salad bar (to stay fit and attractive), if you want them to process energy like mortals. 2) If you want to quickly convince many people to have sex with you, you'd better be attractive as hell. $\endgroup$ – Agent_L Aug 9 '18 at 12:00
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    $\begingroup$ a human sized creature would need to consume a tremendous amount of semen to receive enough calories. A single "event" only yields about 0.7 calories, the average adult human needs about 2000 calories a day, so she needs to sleep with about 3000 men per day. there is not enough hours in day. onlinelibrary.wiley.com/doi/full/10.2164/jandrol.04104. $\endgroup$ – John Aug 9 '18 at 15:47

Warning - answer below might not be suitable for some readers.

Sounds to me like a parasite is the most likely evolutionary track. We can imagine a creature like Cymothoa exigua - but instead of an aquatic crustacean, this creature is an evolved pubic louse that takes up residence in a women's vagina and eats the sperm of any male that mates with her.

Evolution could favor a creature that was able to more closely mimic the vagina itself, or part there of, to better camouflage itself. Perhaps the creature evolves to produce secretions that would promote the male orgasm. Or it could produce pheromones, or stimulate its host to make pheromones that make her more attractive to males. Further, the creature could interrupt the hosts menstrual cycle to maximize its hosts sexual availability and its chances for a sperm meal. The creature could also stimulate hormone production in the host that made her sexual appetite ramp up and tended to make her seek out sexual partners.

While this is not a devil woman itself, the concept is pretty horrifying. If you've a strong stomach, just look at images of the Cymothoa exigua parasite on google, and then imagine the creature that evolves to fit the ecology above....I'm not sleeping tonight.

And, as described, a woman hosting this imaginary parasite would be sensual and powerfully attractive to males, while she herself would be sexually promiscuous. Any male having sex with this woman would experience an overwhelming orgasm.

And of course, we must expect that during sex, the parasite would transfer eggs or larva into the mans penis, which would spend part of their life cycle in the male and then transfer via his ejaculate to infect any healthy woman he has sex with.

And who knows what effects we can imagine for the infected male? Does he suffer a madness? A wasting? Other behavioral or physical changes that could be mistaken for demonic possession or infestation? The overall effects of infection, for both the male and female, might get us pretty close to the tales of the succubus from folklore.

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    $\begingroup$ OMG....this is becoming a Wes craven film pitch.... $\endgroup$ – Jim Aug 9 '18 at 5:44
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    $\begingroup$ This is, given what we know of nature, horrifyingly plausible. $\endgroup$ – Joe Bloggs Aug 9 '18 at 7:15
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    $\begingroup$ There is a reason that a professor during my under-grad said that 'Anything you see in a horror movie, has been done by nature in a more horrifying way'. A difference equally horrifying example that illustrates behavioural change are the ant controlling fungi, $\endgroup$ – Bas Jansen Aug 9 '18 at 9:47
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    $\begingroup$ I actually saw a poster at a scientific conference recently which described a fungus with just this lifestyle. Fortunately it infects cicadas and not humans. $\endgroup$ – brendan Aug 9 '18 at 14:14
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    $\begingroup$ Seems to me, the effect on the infected male, since this parasite can affect behavior and mentality (like other parasites do), would be to compel him to mate with as many women as possible. If seduction doesn't work, perhaps rape will. It could impair his impulse control, so he spends money and goes into debt with hookers, cheating on his girlfriend or wife, sexually harassing co-workers or subordinates, basically loses control of his life and becomes a sex addict, mating with new women at any cost, even his freedom. Wow, I'm starting to think this thing is already out there... $\endgroup$ – Amadeus Aug 9 '18 at 15:11

I am going to expand on my comment on Jim's answer, still using Cymothoa exigua and holding to the same warning for sensible readers.

A female parasite with similar behavior to Cymothoa exigua installs itself on the infected host's tongue. By removing the blood flow, it causes the tongue atrophy, after which the parasite replace its functionality.

Being connected to the host's blood system, it can both have metabolic and hormonal exchanges with it.

It can secrete substances that increase the host's libido and also influence the preferences on the matter of sexual act, making the host more inclined toward oral sex. Physical stimulation of the tongue/parasite causes the release of endorphins into the blood stream, giving physical pleasure to the host.

The parasite can provide a stronger stimulation to the host's partner than the original tongue, and also influence the host's behavior to clench on the partner until the very end. Once semen is released, the parasite absorb most of it through its surface. And while the semen is in contact with the parasite, the parasite releases further shots of endorphins into the host's bloodstream, increasing the chances of a prolonged contact, resulting in longer nutrition for the parasite.

Eggs can be transmitted by simple intimate kiss, and for what is worth the parasite can infect both males and females.

The male of the parasite can be much smaller and install itself in the oral cavity, gathering nutrition in the same way.

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    $\begingroup$ Cue gay incubi. $\endgroup$ – Joe Bloggs Aug 9 '18 at 8:17
  • $\begingroup$ This looks like Pornhub's version of The Bay. $\endgroup$ – T. Sar Aug 10 '18 at 20:27

Contrary to some of the comments, human semen does not contain that many calories (I can't find a reputable source for this I'm afraid, but it's listed plenty of places eg https://jezebel.com/a-complete-breakdown-of-the-nutritional-content-of-seme-953356816). A typical ejaculation contains about 20 calories, so the size of the succubus would be limited to that of a small mammal, unless it can obtain multiple feedings per night. For reference, the Eastern Gray Squirrel of 500g requires 137 calories (https://www.jstor.org/stable/3799379?seq=1#page_scan_tab_contents)

Therefore, I would suggest that any creature that size would not be sexually attractive (to most people!), neither would it be big enough to ambush a human to forcefully harvest sperm (Perhaps they work in packs?!). It would have to either have some sort of secretion or venom that would render its target unconsious or paralaysed, or as suggested, be able to manipulate the dreams of the target and feed on their wet dreams.

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    $\begingroup$ If they work in packs, they have to share the 'food', right? $\endgroup$ – Mark Aug 10 '18 at 20:58
  • $\begingroup$ @Mark Yes, I guess they would - now that's a scary thought! $\endgroup$ – Markyyys Aug 13 '18 at 9:36

Alternative track: I think you're focusing on the physical instead of the traditional feeding. They weren't surviving on the physical result, they were eating the soul/emotion of the victim. The sexual coupling was either to make the spiritual connection (remember, most pre-modern and many modern folks think of sex as a spiritual connection) to feed. In some variants, it was just the bait, and the sex was irrelevant while the demon ate your soul.

If you're going for a less spiritual more "real-world" version of them, think "energy vampire".

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    $\begingroup$ The sex would also be a good distraction while they ate your soul, you would be less likely to notice something going wrong until too late. $\endgroup$ – Loren Pechtel Aug 11 '18 at 3:03

I'm not a biologist, by I love evolution and read a lot about it. As you require "humanoid creature resembling a woman" and "feed only on human sperm" I think:

  • The closer the common ancestor with humans, less time required (and more probably) to converge in human shape.
  • That adaptation is more probably to happen if the ancestors already have some parasitic behavior and adaptation, even more if with humans. So, it just turns from one to another kind of parasitic relationship.
  • Although semen has high concentration of nutrients (specially rare oligonutrients, like Zinc), it's not very abundant. So, at least in the beginning of the drift into a new species, should have low requirement of energy (one ejaculation has 20 calories, 150-250 mg of protein) or maybe feeds mainly with another thing but requires semen for some rare nutrient which can't produce (zinc, vitamin B12); maybe both.

Consider that, I think that an evolution of a bat is a good choice; although probably not the only one.

Imagine that for some time in some place, in which ancestors of current humans and bats coexisted, the last ones have some temporary limitations with their diet.

  1. Difficulties to hunt another kind of prey, made them shift to humans (this already happened).

  2. Some of these have some mutation that tends to feed more from males than females (detection of hormone levels), are favored with a little more blood, increasing survival rates of those.

  3. It is known that in some context pain can cause erection, ejaculation with or without pleasure. AFAIK, this is matter of study, but at a chemical and neurological levels it seems that are very similar. So, we can imagine (I think it's very unlikely but not impossible) that they start to bit man penis while they sleep. Note that vampire bats usually do not perform severe damage, as they have sharp teeth which use to cut and then ingest the blood with their thongs. In this situations, this subgroup has the advantage of more blood and less complications (no bones). In the case of an event of ejaculation, they could have —in addition to blood— the nutrients that are missing.

  4. But, as you can imagine, when humans wake up that would be very unpleasant. So, after thousands of years, they adapt to look (woman) and feel (less pain) more pleasant. And because of that, the ingest of human blood became rare (other animals are less dangerous) and the parasitism with humans tend to the ingest of rare nutrients through semen.

Other observations:

  • Regarding to the size, there are two opposite pressures here: look like a real woman (taller) and reduce energy and nutrient requirement (smaller). So, they should be petite at least.

  • Probably do not have the capacity of reasoning or talking like a human because they do not needed (and it's something very complex). Maybe mumble some words like a parrot can learn (imitating real women and by try-error).

  • As it is risky, probably only pray humans when there is a lack of nutrients, or when the requirement is higher (like pregnancy, as with mosquitoes).

  • Because of the low amount of semen a man can ejaculate, when in need probably feed on many men.

  • As they only look as a woman when needing feed on men, we can think that have many stages of metamorphosis. They lost their wings in the stage of human depredation, and probably in the next stage have something like wings but not so efficient. Also, in some individuals the metamorphosis fails. Both details could be related with emerge of cultural image with arms and wings, but do not have both at the same time.


One form of succubi were ones that stole semen and used it to impregnate women. This could be done if the succubus' vagina was like a hemipenis, that could invert to work as a vagina, and then become erect to work as a penis. This could happen if an ancient society bred a group of humans to impregnate women randomly, perhaps to avoid inbreeding depression

  • $\begingroup$ Excellent but just for clarity's sake, could you describe the action of the hemipenis to your readers. $\endgroup$ – Rottweiler on market-day. Apr 23 '20 at 23:46

If they only attack whilst someone is dreaming then they don't need a full human form. The creature could be a worm that expands as it engulfs the man's penis. A regular undulation along its length will do the trick. On awaking the victim remembers what he imagined in his dream - a seductive woman.

Because of its relatively small size, this explains why the energy needs are low enough to survive on semen alone. A good habitat would be hotel rooms where there is an ever changing supply of victims.


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