Instead of the whole egg laying parasitic vagina concept, which was the leading idea in the original question.

Assuming the succubus is purely the whole woman like creature.

  • Can she gain enough sustenance from sex?

  • And how can that acquisition of sustenance (sex) cause a man to incrementally go insane?

  • Answers need to reconcile body mass with caloric intake based on plausible metabolic rates.

To be clear, this is specifically looking at how this one particular aspect of the succubi could be explained, rather than allowing the whole egg laying concept and looking at the big picture.

  • $\begingroup$ Comments are not for extended discussion; this conversation has been moved to chat. $\endgroup$ – L.Dutch Nov 20 '18 at 19:48
  • $\begingroup$ Changing the tag from science based to hard science basically invalidates all the answers you got so far. And I personally doubt it is even possible to provide a hard science answer. $\endgroup$ – L.Dutch Nov 21 '18 at 3:20
  • $\begingroup$ @L.Dutch it was originally tagged hard science before all but one answer. It was only today modified not to be based on convoluted reasoning, so it's perfectly within the ethos to change it back. If anything most these answers ought be deleted for ignoring it. Anyways I wager i could put out a satisfsctory hard-science answer to this question. I havent yet because the community is absolutely killing any will to do so. Like what is the point in invoking hard science if this is how its gonna be handled. $\endgroup$ – anon Nov 21 '18 at 3:33
  • $\begingroup$ @L.Dutch "I doubt its even possible to provide a hard science answer" well i guess you never will know cuz whats the point in doing it now. Sort of a self fullfilling comment like "guess the church is right since we burned all the heretics". $\endgroup$ – anon Nov 21 '18 at 4:10
  • $\begingroup$ true, and indeed that doubt is personal. Nevertheless science based doesn't cut out hard science answers, while hard science cuts out science based $\endgroup$ – L.Dutch Nov 21 '18 at 4:12

The Succubus receives nutrition like an embryo in a mother's womb. The inner walls of her vagina are lined with soft tissue that is supplied with large amounts of blood, like a placenta.

The male erection is achieved by increased blood flow to the penis, so the energy-rich blood of the victim comes into contact with the feeding-organ of the Succubus.

To ensure sufficient feeding time, the feeding organ excretes a cocktail of psychoactive drugs that increase blood pressure and heart rate and dilate blood vessels (it's basically a natural Viagra), while enhancing the victim's experience and making them addicted to the Succubus. Ingesting these drugs before intercourse increases the effects, so the Succubus initiates more adventurous forms of foreplay.

These drugs cause the victim's body to maintain an erection even after the point of physical exhaustion and release even more nutrients into the blood stream. The extremely increased heart rate and blood pressure may lead to cardiac arrest in older victims. Younger victims who can feed the Succubus for a longer time get addicted to her drug cocktail and seek her out again and again until their bodies are too exhausted to recover. If they are physically kept from seeking out the Succubus, the withdrawal makes them go insane.

Sciency facts

We're talking about a fantasy creature here. Although it might be possible for her to obtain a minimal amount of nutrients, it won't keep a fully grown Succubus alive, least of all during strenuous activities.

  • The placenta of a woman is just enough to keep the fetus alive at the moment of birth. The size of the placenta limits the growth of the baby.
  • The placenta is literally made for the exchange of nutrients between two blood streams that never mix. The human penis is not.
  • Inside the placenta there is a relatively big area where the blood streams of the mother and child touch. A penis has a much smaller skin area and most of it is probably still too thick to allow the exchange of nutrients

Carbohydrate is transported to the fetus as glucose which is taken up from the maternal plasma by the GLUT 1 transporter and transported to the fetus by facilitative diffusion according to concentration-dependent kinetics. Protein is transported to the fetus as amino acids by specific amino acid transporter proteins. Placental lipid transport to the fetus involves direct transporter mediated transfer of certain fatty acids as well as lipid uptake from lipoproteins, metabolic alteration in the placenta, and release into the fetal plasma. (source)

  • All these transporters are missing in the victim's body, so the actual exchange of nutrients is impossible without injecting them first into the victim.

So if you really, really want to, you can give your fantasy creature a fantasy feeding organ and handwave the problems away. If you want to be a little more realistic, you have to go for a much bigger surface area and much thinner skin to leech nutrients from a victim. Like the intestine, which is gross... but more plausible than the penis.

  • $\begingroup$ This is how i was thinking on answering this though you need to back up your answer $\endgroup$ – anon Nov 20 '18 at 14:16
  • $\begingroup$ @anon Had a look at the scioence... doesn't look good for your Succubus... $\endgroup$ – Elmy Nov 20 '18 at 18:11

"Sustenance from sex" and science-based? Hmmm...

The succubus has a very different physiology from regular humans and even regular animals. Its body contains special cells that translate mechanical movement to chemical energy. So when a man performs "physical work" on succubus body, it actually generates glucose and other nutrients. Men can get overstimulated and excercise themselves into exhaustion and nervous breakdown, while succubus woould get only better as the result.

  • 2
    $\begingroup$ Wow... think of the inefficiencies involved. A succubus Would have to spend very little energy and the Male involved would really have to have one hell of an appetite for this to stand even a chance of working. Plus unless the succubus is getting carbon etc from the air she’ll still have to eat something just for the minerals.. hmm.. Succubus plant?? $\endgroup$ – Joe Bloggs Nov 19 '18 at 19:18
  • $\begingroup$ Ha the spring based succubus is a funny idea. But no this does not adress how consumption results in the mental degradation of the man. $\endgroup$ – anon Nov 19 '18 at 19:24
  • 1
    $\begingroup$ @anon that's the "overstimulation" part. It's like someone is getting a lot of caffeine to stay active and awake. Eventually, the body reaches its limits, and many bad consequences for the health may arise. $\endgroup$ – Alexander Nov 19 '18 at 19:34

While the man inserts the penis into the succubus, the succcubus (similar to a mosquito) inserts one or several long, needle-like stings into the man (either through the urethra or through the skin and along the nerve endings in the glans and foreskin). The sting is really long and follows the nerves from the penis to the brain. The succubus consumes whichever part of the brain you find leads to the most interesting insanity. Basically what happens is like dementia, where the brain slowly "dissolves".

Part of the "insane" symptoms stems from the fact that the succubus needs the man to stop moving to be able to insert her sting(s) into the penis. This will make it impossible for the man to achieve orgasm, which will lead to a combination of permanent (over many nights) extreme arousal with a lack of release, which has been known to make many a man go crazy with lust.

It has been suggested that the succubus is most nourished through those parts of the brain that have to do with sexuality, which is why the succubus seeks to follow the nerves from the penis to the brain instead of using another point of entry like the hand (cf. fisting, links to Wikipedia but NSFW) or (cf. facesitting). This theory has not yet been empirically tested, though, as succubi are difficult to catch and no voluntary male test subjects have been found.

100 g of beef brain contain about 25 g of protein or 150 kcal. If a succubus needs about the same amount of calories as a physically active human female (~ 3000 kcal/d), it would have to eat about 2 kg of human brain each night. Even if we assume the succubus is mostly sitting and not physically very active, it would still have to visit multiple victims each night and eat a significant part of each victims brain at each visit. (A human brain weight around 1.3 kg.) Depending on the number of victims the succubus visits per night, her victims would waste away within one (one victim per night) to a handful (multiple victims) of days.

We don't notice the stings of mosquitoes (only the itching from their "saliva"), and the stings of the succubus are almost equally thin. The remaining sensations are covered by the sexual sensations from intercourse and a mild sedative in the vaginal fluids of the succubus.

  • $\begingroup$ "inserts one or several long, needle-like stings into the man (either through the urethra" Oh God... that just sounds uncomfortable and shudder-inducing...! $\endgroup$ – Sora Tamashii Nov 20 '18 at 6:29
  • $\begingroup$ This just seems confused rather than remotely scientifically supported. $\endgroup$ – anon Nov 20 '18 at 14:15
  • $\begingroup$ @anon You cannot really expect that feeding through the vagina can be scientifically supported, can you? The scientifically supported part is which part of the brain is correlated to which kind of insanity (which I'm ready to answer in a follow-up question). $\endgroup$ – user57423 Nov 20 '18 at 19:07
  • $\begingroup$ @user57423 see im willing to bet i could answer this to a level of detail that is in keeping with and or even surpasses the average displayed in hard science tagged questions. But it's simply not worth it to do if the community isnt willing to support that pushing of the envelope. I guess the real question is 'is it worth it to us to try". Personally i would think it would be interesting if mythical adaptations could be scientifically supported instead of ambiguously hand waved. $\endgroup$ – anon Nov 20 '18 at 19:32
  • $\begingroup$ @anon I'm not sure I understand what your criticism is. Do you want me to provide sources for the fact that brain degradation leads to insanity? I thought dementia was a common enough concept that I didn't have to. Or do you want me to explain which parts of the brain are related to which kinds of insanity? That would be a bit to broad for a lazy sod as me, but I'd be willing to go into more detail if you provided information on what kind of insanity you were thinking of. Or do you lack scientific support for the "stings"? Well, any answer to your question will have to do some handwaving. $\endgroup$ – user57423 Nov 20 '18 at 21:12

The way I allways imagined succubi feeding is they produce a cocktail of narcotics and aphrodisiacs that cause their prey to begin to dedicate all of their bodily functions to semen production. The semen that a man produces while under the effects of a succubi's toxin will be fortified with vitamins and other nutrients that the succubus needs to survive. So I guess I would be more accurate to say that at some point instead of ejaculating semen they instead will begin to output a nutrient rich slurry of their bodily fluids. At some point the succubus will inject a potent acid that will dissolve the muscle and organs as well leaving their "lover" mere skin and bone.


She could have corrosive metabolism that drains a high concentration of sodium (and other electrolytes) from the system. The absence of sodium in the victim could cause brain swelling and any number of indirect side effects that could whither an individual both mentally and physically. On the flip side she could drain moisture, sucking out all the fluids from the body rather than the blood specifically.

On a more abstract level she could be draining the energies generally associated with acupuncture and other schools of Eastern medicine. Draining targeted energy levels could disrupt the balance and flow of chi etc causing symptoms that would not be easily identified by most doctors.


It's not that she feeds on sex alone. She eats stuff, just like we do.

But the succubus has no teeth (this makes her fellatio a unique experience, but that's neither here nor there). She swallows (( ͡° ͜ʖ ͡°)) stuff whole.

She has a gizzard, much like birds do, and she swallows stones as well. But her gizzard is not as muscular as a bird's.

So when she is banging someone, she is also banging stones together in her pouch. As she grinds you, the food in her belly is ground into digestible its. She evolved in this way do that she can save energy otherwise spent for digestion - and saving energy is always a plus for evolution.

Given this, her partner doesn't have to be a man. It may as well be a woman, a laundry machine or even a horse (so she can ride while she rides). Most succubi do prefer men, though.

As for how she drives her partner crazy: she totally charmed you and you weren't thinking straight when you let her climb on top of you. Once the blood gets back to the top head... What is seen cannot be unseen. Have I mentioned that she is toothless?

I know you wanna hit that

  • $\begingroup$ Ha ha ha, i do got to give you props for asserting succubi are teethless to improve filatio. Its not a bad plausibility. Anyways the question clearly asks how can she sustain herself from sex. Offsetting caloric cost with food pretty much contradicts the question. $\endgroup$ – anon Nov 21 '18 at 17:22

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