Vampires are no exception to the phenomenon of evolution. In my world various species or races or breeds of these creatures can be observed. They can interbred as much as neanderthals can breed with sapiens or French men with Saxons or coyotes with wolves. Which means easily and with no ill effects.

They are not mystical creatures, lacking the magical powers usually portrayed in books and movies.

Yet some cultures of vampire can do feats which might seem impossible to the top level elite human.

One city in my world, a multicultural human-vampire city has a formidable military force of vampires. They make for excellent warriors due to their innate tolerance to cold climates, endurance, night vision and being able to quench their thirst and fill their bellies with the flesh and blood of enemy lines. And some say that an army marches on their belly. On top of everything, the weakest vampires can also surpass top human athletes both in strength and power.

But in time of peace warrior vampires still need to be fed. They require only 350 grams of blood per week to maintain idle activities. Fighting and other heavy work increases the thirst.

Vampires in this city are not slaves, they can decide to not be warriors. But there's little to no incentive to not go to war, especially since warriors are paid in both coin and blood taxes.

These vampires are weaker than other "breeds" of vampires but require less resources. Conflicts between warrior vampires and other vampires are rare but it's always a fight of numbers versus quality. Outcomes are never easily predictable.

I have many questions to make, but I'll split it in multiple threads.

First question:

What is the ratio of human citizens and vampire citizens the city must have in order to feed all warriors? The more vampire warriors, the better is the city protected from foes. This also increases the blood requirements thus human cost of shelter and feed.

Also consider that in cold climates blood can be stored for an entire year, but there's a weaker agricultural production.

Extra details:

Vampires can breed only with other breeds, races, cultures, species of vampires not with humans. The first section might be confusing but I thought it will be useful in the fure to connect the next questions I'm planning to make.

Vampires can ingest other foods as a hobby to savor the taste, but they only require human blood to survive. Human flesh is often eaten as filler food during war.

Vampires are born from sexual reproduction, not created.

Vampires are humanoids but not related to humans. They look like humans due to convergent evolution. The same way the ancient reptile Ichthyosaur looks and behaves similarly to the mammal dolphin even though they are not closely related or how bats and pterodactyls evolved similarly.

Some types of vampires are photosensitive and nocturnal, but those vampire warrior specifically can sunbathe if they want.

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    $\begingroup$ Welcome to the site and a good start for your question, but we will probably need a few more details about your Vamps. First, is animal blood a viable solution? Can they ingest things other than Blood at all? Even more importantly, how does Vamp reproduction work? Is it Viral? Is it a dominant Gene? Is it Recessive? This is all going to have an impact. If its a recessive gene then little Joey may just be a kid who needs a little supplement once a week and when he graduates high school He'll get a few extra calls from military recruiters. If Viral, there would new set of criteria $\endgroup$
    – Paul TIKI
    Commented Apr 13, 2021 at 17:37
  • $\begingroup$ @PaulTIKI added new details $\endgroup$
    – user84912
    Commented Apr 13, 2021 at 17:58
  • $\begingroup$ Should be "They can interbreed". "Inbreed" means breeding with your relations. $\endgroup$
    – Daron
    Commented Apr 13, 2021 at 18:30
  • $\begingroup$ Cool, this tells me quite a bit of what I want to know.. One other bit that may have bearing. Do your Vampires just dislike Sunshine or do they burst into flame. We know they are not Human, but the "Other" factor is important when looking at the politics of various situations. Another, very important factor is your tech level. Is the setting far future cyberpunky or is it sometime around the battle of hastings. Each will add it's own things to consider $\endgroup$
    – Paul TIKI
    Commented Apr 13, 2021 at 18:32
  • $\begingroup$ @PaulTIKI they have no problem with sunlight. $\endgroup$
    – user84912
    Commented Apr 13, 2021 at 19:16

4 Answers 4


2 vampires for every 1000 humans.

Let us work backwards from the Aztecs, a society that practiced large scale human sacrifice. We will have your society have the same amount of human sacrifice but all sacrifices are used to feed vampires.


Michael Harner, in his 1977 article The Enigma of Aztec Sacrifice, cited an estimate by Borah of the number of persons sacrificed in central Mexico in the 15th century as high as 250,000 per year which may have been one percent of the population.

250000 being 1% means a population of 25 million. Assume you have a similar population. If every one of these 250,000 sacrifices is used for blood then that is 250,000 x 5000 ml blood each = 1250000 liters of blood a year for vamp feed.

1 gram blood = 1 ml. Vampires need 350ml /week when idle, more when active so I will say average 400ml week; 400 * 52 weeks = 20800 ml or 20.8 liters per vampire per year. 1250000 available liters /20.8 liters = 60096 vampires can be sustained by this number of human sacrifices. 60096/25000000 = 0.00296 or 0.29% of the population. 2 vampires per thousand humans. Or 2.9 if you allow fractional vampires and I think you should. Maybe those ones are short, or missing parts but I like to think they suffer no discrimination for being fractional.

As regards where these sacrifices come from, the Flower War method sounds like a good match for your warlike society. Read up: https://en.wikipedia.org/wiki/Flower_war

You have me thinking now about an Aztec society in which sacrifices are used to feed vampires. Pretty cool. And when I go out Flower Warring to collect sacrifices I would definitely want some of my own bloodsuckers along with me. I think vampire on vampire combat is going to happen in these contests. When I see the enemy vampire coming to capture me I am definitely going to run toward my own friendly neighborhood vampire (we call him Sucko) as fast as I can. Hopefully everyone around settles down with the warring to watch Sucko bust out his moves on that jerk because that is the most fun part of Flower Wars.

  • $\begingroup$ A minor calculating error: 60096/25000000 = 0.00240 or 0.24% $\endgroup$
    – Nosajimiki
    Commented Apr 14, 2021 at 21:19
  • $\begingroup$ @Nosajimiki - I think the original was more humane. A 90% fractional vampire could get by but a 40% would be ...lacking. $\endgroup$
    – Willk
    Commented Apr 14, 2021 at 22:03
  • $\begingroup$ Lol perhaps, but if you think of it as how many humans you need to feed a vampire, you come to needing 416.00 humans. No strange body parts left over. $\endgroup$
    – Nosajimiki
    Commented Apr 15, 2021 at 13:26

~56:1 Ratio Using Blood Taxes will be Most Common

A single unit of blood is 525 mL which a healthy donor can give about once every 8 weeks. This means you need 5.3 healthy donors to support a vampire. The caveat here is that not everyone can be a doner, so you will not be able to just say you need 5.3 humans per vampire. The old, the young, the sick, the pregnant, and people with certain disorders can not safely donate blood. This number could be even smaller if your Vampires are at risk for bloodborne diseases like HIV or hepatitis. According to the Red Cross only 38% of people are eligible blood donors.

Using these figures, your ratio of vampires to humans will depend a lot on how you are getting the humans to participate in these donations.

  • If blood is only harvested from volunteers then you will only get about 1/200th of this capacity based on current volunteer blood center figures giving you ~2800 people per vampire.

  • If you do a paid volunteer system, then you get about double that assuming you pay your volunteers the current market rate of 20-50 USD per unit. This yields ~1400 people per vampire. That said, the more you pay for blood, the more volunteers you will probably get. An average human spends ~140 USD/week on groceries meaning the value of a unit of blood in a vampire society is more like 210 USD. I can not predict how much this will increase your supply, but I suspect it will be significant. I would ballpark this system putting you in the 500-1000 humans per vampire range.

  • Human sacrifice following Willk's Aztec model will give you ~416 humans per vampire. While his idea definitely wins the cool contest, the fact that it is less efficient than the following models without being any less cruel makes it pretty unlikely for any civilization to go along with IMO. The Aztecs did human sacrifices because they believed they would all die without appeasing the gods. Vampires on the other hand are known to be mortal in this setting, even with their superior physical prowess, Vampires would have a hard time stopping a human uprising that outnumbers them over 400 to 1.

  • Next, you mentioned a blood tax. How a blood tax is levied will require a lot of consideration but can yield a lot more vampires than previously mentioned methods. Blood donations make a person weaker and more prone to sickness. If you try bleeding everyone at their maximum capacity, then your human workforce will not be able to do any heavy labor for itself. This makes important tasks like farming, construction, etc. unsustainable. To this end I would suggest limiting the blood tax to 6 donations per year. This gives every human 9 healthy months, and 3 months a year where they will be weakened by their donations. Most professions, particularly those than involve heavy labor, have a down season. In winter your farmers can donate. In summer, you'll get a lot of contribution from teachers and outside heavy-duty laborers. Then in spring and fall you collect taxes from your white collar and light duty laborers who don't really need to take an off season. Using a responsable blood tax like this, I would estimate a population of ~56 humans per vampire.

  • Your next most aggressive option is to keep humans as livestock. In this case you can bleed them year round since the Vampires would be doing most of the work of sustaining the humans. In this case you will get somewhere around 10-14 people per vampire depending on how aggressively you cull your herd. Keeping in mind that even with aggressive culling, you will still have a significant number of humans who can't donate at any given time because they are either children, pregnant, or acutely sick.

  • Lastly, you have your most aggressive option where you keep humans as slaves. In this case you only keep humans that can actively donate year round, and when they die, you go out and get more. This will give you about the 5.3:1 ratio.

Considering that different societies will probably experiment with various techniques, you will likely see those that pick better techniques drive others out of existence. Volunteer & Paid Volunteer methods would allow for a large healthy human population, but very few vampires; so, they would be at risk of being conquered by smaller civilizations with more vamps. Human sacrifice would cause major discourse between the humans and vampires. The humans being so much more numerous than the vampires could easily overthrow their blood-thirsty masters at which point they would probably have to merge with another civilization that sustains more vampires more humanely, or be conquered by one that allows a smaller human to vampire ratio. Keeping humans as livestock makes sure that the humans stay few enough in numbers that they can not rebel, but humans take a lot of work to feed. Your vampire society would be forced into sustenance level conditions putting all of their work into producing enough food for their humans. Such a society would be kept from technologically advancing until it is overwhelmed by superior technology. Slaving means you don't have to work too hard to keep a viable human population, but you'd be reliant on needing a constant source of "wild" humans to replace your attrition. Here, your vampire society would need to be so constantly at war that they will eventually have enough enemies that they are taken out.

This just leaves blood taxing. Blood taxing allows human societies to grow large and self sufficient while also maintaining a large population of vampires. In the end, most nations will probably turn to the blood tax method or be wiped out for one of the afore mentioned reasons.

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    $\begingroup$ My next question was about a similar kingdom where vampires don't share power but dominate humans, using them as livestock. Nice prediction. $\endgroup$
    – user84912
    Commented Apr 13, 2021 at 18:03

You have a few things to consider first. How do the Vampires feed under normal circumstances? Does it have to be human blood? You already mentioned that in colder climates blood can be stored, so I am assuming it does not have to be purely fresh.

The whole point is that your Vamps, as a different species, are what would be called "The Other" They are different than us. They are not like us. Why should they Rule us? This happens all the time, even in modern society, when "The Other" is still the same species, just a different skin color or religion. That means the Vamps are going to have to downplay the bits about them that make them seem inhuman. No showing off superior strength unless you have to. Don't drink blood in front of humans. Come by the backyard BBQ. Don't gravitate towards positions of power and do not abuse that power if you have it.

I would guess that you would want your vampires to be around 1% of your population. this might be lower than the human population could actually handle if this was a pure predator/prey situation, but remember they have to live in at least some sort of harmony. Asking someone for a 500 gram donation to the blood pool once every year and a half (I'm accounting for minors not being eligible to donate) is not so onerous as to cause revolt of humans against the Vamps. You also want to make sure the donation is impersonal, like a modern day local blood bank situation. That will be far more tolerable that having to go somewhere to have somebody chew on your neck.

In the case of a sudden attack, the vamps will always be in slightly better than subsistance level feeding conditions. Of course, then they will have victims to eat, so you would be even better off. In the case of a war, you could ask for a lot more blood to be donated without harming your populace, but you have to be very careful in not extending the heightened levels beyond what is actually needed.

Other Societal notes: Make sure that if a Vamp gets to a position of power and authority, they do it through open, honest, and merit based means. Make sure all vampires are subject to the same laws as everyone else. As a matter of fact, Hold them to a higher standard. Make military service for a Vamp mandatory for at least a couple of years before leaving them to make the choice whether to continue to serve or not. You want to take away the arguments for the Vamps being Other as much as you can so you can integrate them as deeply as possible into your society.

  • $\begingroup$ Gallic and other northmen were considered a different kind of humans by the Romans. Yet roman people were a minority in roman armies. $\endgroup$
    – user84912
    Commented Apr 13, 2021 at 20:22
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    $\begingroup$ @Thera True. The Northmen scared the bejeebers out of the Romans when they were first encountered though. There was also a lot of skullduggery going on with promises of citizenship, and actual landowners losing their properties because they were out on campaign. It was a mess come the end $\endgroup$
    – Paul TIKI
    Commented Apr 14, 2021 at 13:16
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    $\begingroup$ @Thera "Yet roman people were a minority in roman armies" This is only sort of true depending on the exact date and definitions you use. It was not really until the late 1st century that you started to see the Auxilia become more numerous than the Roman Legionaries. But since we are talking races, not nationality here, it should also be noted that most Auxilia were from the Greek provinces which the Romans did not consider to be a different Race. Greco-Romans were always the dominant race in the Roman army. $\endgroup$
    – Nosajimiki
    Commented Apr 14, 2021 at 17:26

I'm trying a scientific answer for the fun of it, but you threw me a curve with the "resistance to cold".

A fairly well known study tried to estimate if dinosaurs were cold or warm blooded based off of the ratio of predators to prey in the fossil record. I put a good overview below, but a short take away is that as cold blooded predators require far less energy and eat less, the ratio of predator to prey can be close to 1:1, while for warm blooded predators the ratio may be more like 1:10.


The curve I mention is that cold blooded animals are most certainly not resistant to cold. Otherwise, the vampires could fit this description nicely. They would have to be relatively inactive most of the time, but be capable of enormous feats for short periods when needed. (think alligators on the hunt) I'm not sure how far I would take it, but this could form a sort of symbiotic relationship where the humans are industrious workers, but the vampires are a real terror on the battlefield and can end rebellions.

  • $\begingroup$ That's tempting idea.....I guess they are not going to conquer Russia any time soon. $\endgroup$
    – user84912
    Commented Apr 13, 2021 at 21:22

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