So, I know I haven't posted in forever, but a bunch of things happened so I didn't, so I'm coming back in with a bang. This is an approximately 5k explanation of the lore, worldbuilding, and biology information I couldn't fit into this vampire Jaskier fic I wrote for a gift exchange. I really hope you enjoy it. Also, for clarity, I used lowercase; higher vampire, when talking about all sentient vampires, alps, bruxa, etc, and capitals; Higher Vampire, when talking about the kind of vampire that Regis and others are.
The first time I started deep diving into Witcher vampire lore, and coming up with my own, I came up with a general idea for their previous world before they were brought to the Continent by the Conjunction of spheres, based on their traits. For one, the vampire's size, approximately the same as humans, is extremely unique among sanguivores (animals that feed on blood). Almost all of the species who do so are bugs and insects, which are many many times smaller than the animals they feed on, both for sneaking the blood so the provider of the blood doesn't notice, and so they can feed multiple times on the same victim with no problems (or, in the case of ticks, stay on the victim for as long as they live without having to find a new host because of lack of blood). Of course, there are many exceptions, like several kinds of lampreys that feed on fish that are similar sizes, or slightly bigger than them, (though they feed on other body fluids as well, not just blood) or the white-winged, and hairy-legged vampire bats, which are about the size of a mouse, and prefer birds, including domestic chickens. But those are exceptions, and so I figured that it was likely that in their original world, they fed on creatures far larger than them, maybe something similar in size to the biggest dinosaurs.
It's also likely that that world would have lower gravity, which would assist in making it possible for the giant creatures they fed on to move around and support their own weight (like the ocean does for large whales, and is part of why sea creatures can grow so much bigger than land creatures) and also make it easier for the vampires to leap up high enough to get blood from them. Sanguivores need to have very good mobility to feed from their much larger prey, so most of them are able to fly, or at least jump extremely high. An example is fleas, which can jump up to 150 times their body height. In the higher gravity of the Continent, their jumping skills would be much less impressive, but they still have much more speed and strength than any other humanoid species on the Continent.
When I started actually researching sanguivores in order to write the story, I found out something very interesting. Animals that feed purely on blood usually have to drink much more of it than other similar sized animals have to eat of other foods. Blood is not a nutritious food source at all. It is approximately 95% water, and the rest is mostly protein, with a little bit of sugars and a tiny bit of vitamins and minerals. If you assume that the vampires have a similar need for calories as a human, they would need to drink approximately an entire full grown human worth of blood every single day. In modern times, it wouldn’t be much of an issue to stay unnoticed in a large city, even for quite a few vampires, because of the sheer amount of humans that go missing or are murdered each day. However, on the Continent, which would likely be similar to medieval times in our history, it would be significantly harder to be a vampire without arousing suspicion, as populations are smaller, and also far more spread out, making it very easy for people to notice that people are being taken, especially if they're feeding off an entire person each day. They would also need to travel a lot to be able to feed before being driven off. And that's just for one vampire in the area, any group of vampires would have to travel very often to accommodate their need for blood, which is probably why most vampires travel alone, and tend to be rare in the games. Except for the vampire brothel in the games, where blood can be exchanged for sex, making it far easier for multiple vampires to survive in one spot.
Of course, cattle and other large animals have about 6 times more blood than humans, which would make it easier, and far more likely to find them in the wilds, where there would be no contracts, and where Witchers would be less likely to find them. This is helped by the multiple large monsters in this world that they could feed on, like wyverns, griffins, or even kikimores! Of course, it seems that most of their skills seem fine tuned for feeding off humanoids, and most mentions of them have them only feeding on humanoid blood, but I will discuss that later. The thing is, there seems to be a lot more vampires around Toussaint, as in Blood and Wine, there were enough to completely overrun the sizable city of Beauclair, with mostly farmland around it, and not many wild areas for vampires to hide. What was their source of blood that so many of them could live unknown so close to the city?
Part of the reason creatures that feed on blood are pervasive in so many cultures, is the more metaphysical aspects of blood. It was often seen as a source of life energy, a type of magical energy that was unique to each person, and the source of much of their energy, which is why most cultures have some sort of blood magic, and often used blood as a signature of sorts. This is sort of similar to how succubi and incubi are said to feed on life energy, through the method of having sex with people. If vampires were feeding on the more metaphysical life energy as well as the actual calories that blood gives them, it's more than reasonable to assume it would reduce their need to feed, so they don't need to drink an entire human per day.
I mentioned in the story that blood from the veins and blood from arteries has different properties for the vampires that drink it, so I thought I'd provide an explanation here. Arterial blood provides more instant energy, and venous blood provides less, mostly due to the circumstances in which it is taken. For vampires who don't want to hurt their donors, taking from an artery would be dangerous and far more likely to be deadly because of the combination of the fast pumping artery (depending on the artery and how badly it's injured, you can bleed out from an artery in under a minute) and their anticoagulant venom. However, if you're fighting someone, not only will your heart beat faster, pumping blood out of the wound faster, but you also get a dose of the adrenaline pumping through your veins, giving a vampire an even bigger advantage if they can process the adrenaline quickly. (Just about every animal on earth can make and process adrenaline, so if the vampires are close enough to be able to process human blood, they can probably also process adrenaline). But if they're taking from a slow pumping vein, the process of taking blood will be calmer and slower, and without the adrenaline of fighting or having sex, the painkillers in their venom would have greater effect, and probably calm the person even further.
But that's not the only reason arterial blood has more energy in my universe. I was thinking about how the life energy vampires also feed off would work, how in lore, it's finite (can die if enough is sucked out of you) needs to be carried in the blood so vampires can access it, but also be accessible to succubi and incubi, who also feed off it. For that, I'm associating it heavily with blood. And because in the past, the heart was seen as the center of the mind rather than the brain, I wanted to incorporate that, and have the heart be the source of life energy. So arterial blood, fresh from the heart would be full of life energy, while venous blood would be empty of it, going to the heart to be refilled. So arterial blood would be a better source of energy, but also far more dangerous to the donor.
Note; while many stories of vampires that feed on humanoids have them have a venom/saliva with coagulation properties (to reduce blood loss and death after feeding) every sanguivore that I know of on earth has saliva or venom with anticoagulants, to ensure that the smaller blood vessels they're feeding off don't close so soon after opening. If vampires originally fed on animals much larger than humans, they would need anticoagulants for the same reasons as creatures like mosquitoes. To have the properties of their saliva change to the exact opposite effects is extremely unlikely when it would probably do nothing to help them, and probably take thousands of years to develop.
Vampires feeding off life energy as well as blood could also explain why, 1) they seem tailored to feed from humanoids, because I believe that humanoids would have more life energy than animals due to their sentience, so human blood would give them more energy, and 2) why higher vampires only get drunk off of the blood of sentient beings, (I cannot find a direct quote to either contradict or confirm this, feel free to let me know if I'm wrong) because it provides something extra that animal blood doesn't. Of course, even with that, it would still be hard to maintain a consistent blood source, especially if they don't care about human lives and kill every human they feed from.
The dramatically higher density of vampires around Toussaint must have a cause, and I believe that cause is some kind of vampire community in Toussaint, where they work together with humans to get the blood they need. I believe there must be a vampire noble family of some sort ruling over the area, so the human nobles believe that the area is under control and that they don't need to visit. I'm going with this idea partially because I'm keeping Jaskier’s (a Higher Vampire in the story) background of being noble born, and partially because Orianna was a very rich and well thought of vampire, that seemed to be a noble of some kind, possibly connected to Jaskier’s parents. Also, a place where vampires could live freely with humans would almost certainly have to be ruled by vampires, as in the world of the Witcher humans would never put aside their prejudices enough to let that happen.
This community would probably be extremely careful about keeping themselves away from any attention from Witchers, killing dangerous monsters in the area and policing their own to make sure no rebellious teenagers (like Regis) go wild on blood and attract attention. I bet that once the group that pressured Regis into blood drinking was found out, they were killed or driven out so they wouldn’t attract attention from Witchers.
I believe that Regis was a part of this community partially because I wanted him and Jaskier to know each other, and partially because his name means kingly or regal, which added to the sheer amount of names he has, similar to traditions of the British royal family, heavily implies he's a noble of some kind, possibly Jaskier’s cousin, and was supposed to be the heir until Jaskier came along. It could also go well with Dettlaff's distant appreciation of him, never getting up the courage to talk to someone more noble than him. Another reason I believe Regis was a part of that community is that he was once in a relationship with the Queen of the Night, who later became the Madame of a brothel that offered sex for blood, offering the same kind of stable food source and safety that the vampire community could. Maybe she was even inspired to set out on her own to create her own community by Regis' addiction, wanting to make more safe places for vampires to live without needing to kill.
The community would likely have the non-vampire villagers pay their taxes mostly in freely given blood rather than goods or money, (though some goods and money would be necessary to pay the taxes of the nobles above them). I also believe there would be a lot of innovation, medical and magical in that kingdom, because of the blood need. The vampires would likely be able to detect illness, deficiencies, and other medical issues that can be detected in the blood, which would likely lead to impressive medical care that anyone can access in that kingdom, both due to them having more knowledge about blood and the body, and due to a vested interest in making sure the blood they feed on tastes good (it would be a very likely evolutionary advantage to make healthy blood taste good in order to make sure their only food is giving them everything they need, and not hurting them, like how rotting food usually tastes/smells gross). Magical innovation would likely be because they would be searching for some way to multiply blood, or remove their reliance on it entirely, also working on a way to reopen the portal to their home world. All that would explain why there are so many more vampires in Toussaint than anywhere else.
Now for my explanation on how vampires as a species so easily switched from feeding on creatures much larger than them, to primarily feeding on humanoids. I believe that the lower varieties of vampires, the ones that are not sentient, are more likely to live in the wilds and hunt creatures rather than humans, while the sentient ones are more likely to hunt humans, just due to the amount of skills that seem specifically tuned to hunt humans. These skills are very common in the sentient ones, but always seem absent in the non-sentient ones, skills like telepathy, shape shifting, the intelligence to blend in as a human, usually a better resistance to the sun, and invisibility to magical scanning.
We all know that Higher Vampires each have a unique power, like Dettlaff's power over lesser vampires, and the possible variety of powers is unknown, possibly every power you could ever think of, and that makes Higher Vampires an extremely adaptive species. The only disadvantage is the very low numbers of them that we know of, despite how hard it is to kill them. This makes it likely that they have extremely low fertility, or very long reproductive cycles, making children a very rare occurrence. This makes sense with their impossibly long lifespan and invincibility unless killed by another higher vampire, as otherwise, the whole world would be quickly overtaken by higher vampires, even over other vampire species with the fact that they do not need any food/blood to live, so there is no need to have many children.
However, it's very likely that they can interbreed with the other higher varieties of vampire. They all have many similarities, both physical and in their abilities, so it's likely they can interbreed like humans and Neanderthals could, and it's likely the cause of all of the sentient vampires being able to blend in with and hunt humans so easily. If they previously drank from creatures far larger than them, the ability to look more like a human would be completely useless, only making them more vulnerable with a lack of claws and teeth, and I speculate that vampires were the only humanoids in their original universe, given how most of them don’t see humans as more valuable than prey, not accepting them as other sentient beings. Much like the humans in the Witcher universe actually! So they had to find a way to blend in, and fast, because humans already had legends of evil blood drinkers, and were fully willing to kill them.
The source of vampires ability to shape-shift and use telepathy was likely higher vampires who had those abilities naturally, and interbred with the other sentient vampires, passing the abilities along so quickly due to the environmental pressure to blend in, especially as humans began mutating the ability to use the Chaos in the new universe, and start to hold their own against vampires. Especially because they had to adapt to the higher gravity of the new world, and lack of their traditional food source, so they would be at a disadvantage, whereas humans came from a very similar world and could easily use their previous knowledge in this new world. And the cause of higher vampires breeding so rapidly and easily with the other sentient vampires? The intoxicating abilities of human blood. Even if they wouldn’t breed with them usually (for cultural reasons I suspect, which I will share later) the sudden ability to get intoxicated, and their sudden removal from everything familiar would likely combine to make them want any kind of connection and closeness with familiar species as they could, making it easier to breed important survival traits into the different species very quickly.
However, some of the higher vampire species are weirdly different from each other, other than the abilities that make it easy to hunt humans. One major thing I found though, was that mula, Higher Vampires, katakans, and nosferats have both a very humanlike, and a very batlike form (the only semi-official image of a mula I found looked somewhere in between the two, so that could be either an inbetween form, or it's only form, but apparently it can look very similar to other vampires in their human form, so it likely does have both forms, and the one image was just in an inbetween form) and bruxae and alps have a very humanlike, female looking form, and can shape-shift into a full animal, like a large bat or cat. (Sidenote; it is specifically stated in the Blood and Wine bestiary that alps can turn into animals, though it is not mentioned anywhere else. As for bruxae, there is a scene in the books where a bruxa turns into an "enormous black bat". This could be interpreted as a humanish bat form like many other vampires, but in the translation I read, it seemed like it had no humanoid features in its bat form, never standing upright like a human, and having full, working wings instead of the more humanlike arms in all other higher vampires batlike forms. As far as I know, only Higher Vampires of the higher vampires have full wings they can use to fly in bat form. The bruxa could partially transform back into a human, like how other higher vampires have in between forms, giving it a few humanoid features, but it was described as distinctly different from its fully batlike form, so the full bat form is clearly not at all humanoid)
This sharp difference in its shapeshifting and forms despite the fact they can interbreed heavily implies either sexual dimorphism so strong that they appear to be entirely separate species, or that they are separate species that regularly interbreed, with some of the species being entirely one sex. Of course, it's possible that the purely female appearance of bruxae and alps is just a part of luring humans in, and both males and females of the species look like female humans when in their humanoid form, but it's 1) a little harder to fit into the ideas I have, and 2) less likely that Higher Vampires would interbreed with them, thus making their ability to all disguise themselves a little less likely. And 3) a lot of the lore of this story was heavily inspired by the worldbuilding of this fic, so I wanted all the alps and bruxae to be female.
I do find it unlikely that bruxae and alps wouldn't have a batlike form like all the others, as it seems like they have a more humanlike form, as well as being able to look more distinctly like a vampire, with longer nails and teeth, but still mostly humanlike. This could be their more batlike form, but it's more likely to be an inbetween form. They would also probably have a true form in their original world before they could disguise themselves as humans, so I believe that they do have a more batlike form that we've never seen in canon. Maybe they can only bear young in their batlike form, which would make them more vulnerable and also harder to hide amongst humans, so they may hide away in the wilderness, possibly getting mistaken for other species with a known batlike form.
In the wiki, the mula is only referred to with male pronouns, and Higher Vampires, katakans, and nosferats seem to be both, reffered to with neutral pronouns, with none of them being able to turn into an ordinary animal, though Higher Vampires and mulas can turn into a mist form instead. (Fun fact, Higher Vampires having a mist form is only seen in cutscenes in the games, and that fact is not in the wiki. This gave me a panicked moment in the last phases of editing this, where I thought this entire part was heavily based on some widely accepted fanon. Fun times.) And funnily enough, the only higher vampires we know of are all male, (and in my story, including Jaskier) though they are referred to by neutral pronouns in the wiki like the other species that can be either male or female. Maybe because of each one's unique abilities, they can be female very rarely, with males being much more common, which would also make it possible for them to breed within their group, fitting the cultural aspects I came up with.
Because of all of this, I believe that they are a heavily sexually dimorphic species, except with males, females, and hermaphrodites instead of just males and females. It's possible that katakans and nosferats could be either sex instead of hermaphrodites, but that would make the sex chromosomes more complicated, so I'll stick with the simpler option. Another option is that they are separate species that can interbreed, but as the most well accepted definition of species is that it is a group that can interbreed and have viable and fertile offspring, so having multiple species that easily interbreed and pass genes between them and through generations makes it unlikely that they are all separate species by our definition. (Of course, in our world, some species are considered different species because they can't interbreed purely due to living in different places, and the Conjunction could have gotten rid of geographical limitations, making them technically different species, but I'm going with Occam's Razor for this) So the way I made it is that females (bruxae and alps) have the ability to turn into other animals like bats, cats, or other animals, while males (Higher Vampires and mulas) have a mist form. But katakans and nosferats, getting both genes, wouldn't be able to do either, needing two copies of one kind of transformation gene to be able to do it. Also, both katakans and nosferats are the only higher vampires that are susceptible to the sun (except for alps, but it doesn't seem to actually hurt them, just tan them very darkly), so that's a gene that is probably connected to the sex chromosomes in vampires.
I was also inspired by the side blotched lizard, a species with three varieties of males, each with a different set of markings, behaviors, and mating preferences, which shows that you can have distinct varieties of a sex within the same species without them combining, making the two varieties of each sex of higher vampire perfectly viable. So females would need two female genes, males would need two male genes, and the hermaphrodites would have one copy of each. Thus, Higher Vampires could breed with almost all the other types of higher vampire, passing on their adaptations for the new world, except for the mulas. They would only be able to pass it on to a hermaphrodite variety, which could only then pass it on to the mulas, which could be a good in-universe explanation for why they are so rare (aka, are in none of the games, and are only mentioned once in the books), because it took longer for the gene to transform into a much more humanlike form to pass down.
Almost all of this is pure speculation based on other ideas about them I came up with, because there are very few facts about it on the wiki. We know that all intelligent (higher) vampires celebrate full moons as an important holiday. We know that there are three different tribes of vampires that live in different places. That's about it. So I'm doing a lot of speculation here. For one, I believe that there is some kind of higher being/god that they believe in and worship, likely tied to the full moon. It seems unlikely that the being they worship would be an Unseen Elder, as it is shown that even Higher Vampires are terrified of disturbing them, and full moon celebrations usually consist of raiding villages and getting drunk on blood, and given that bruxae are said to sing shrill and sickening songs after they drink blood, I doubt they're trying to worship the unseen elder, who we know does not like disturbances or excessive conversation. However, I do believe that Higher Vampires, especially the Unseen Elders, are seen as the favorites of that god, much like prophets, saints, and the Pope are seen in Christianity. The scene in Blood and Wine where Geralt talks to the Unseen Elder seems to imply that only the elders are allowed to decide that a Higher Vampire can be killed, and even then, the vampire who did the killing is still ostracized, which makes it even more likely that Higher Vampires are fairly rare, and also revered in some way. Their power over all other vampires would also cause them to be seen as blessed, or just better than any other kinds of vampires. (Dettlaff having the power to control lesser vampires makes it likely that he has the possibility to become an Unseen Elder, because as Higher Vampires get older, their powers grow, so I assume that if he gets old enough, he would be able to control other Higher Vampires as well. This could also explain why the Unseen Elder is willing to help Geralt with Dettlaff when the direct threat to him seems minimal to us, because Dettlaff has the potential to usurp him in the future). This power, the other random powers they could have, and their near invulnerability, would make it easy to think that they are the most favored of whatever deity they worship, and thus the most superior kind of vampire. Even the fact that they have no need to drink blood like any other vampires could contribute to the belief that they are better somehow, more spirit than body. Like how in many religions there are fasting rituals that supposedly bring them closer to their god or gods, or stories of people so close to the gods that they didn’t need to eat at all.
But all this would make Higher Vampires feel superior, and want to breed only within their own type, much like medieval royal families (the infinite lifespans and the rarity of children would lessen the impact of inbreeding). But for that to happen, they would either need to have Higher Vampires that can birth children, which could be possible due to the wide array of powers they can have, and real world sex differentiation being more complicated than you think, like bird species that usually have two sexes having an animal be half male and half female, both gonads being functional, or they pull other types of vampires that can bear them children into the "royal family" to have children for them, likely a combination of both.
Also, in the vampire language, they likely have three or four gendered pronouns instead of the three in the English language, (depending if they have a neutral pronoun or not) masculine, feminine, neutral, and ones referring to the hermaphrodites. This makes it likely that they are more likely to accept trans and nonbinary vampires than humans would, especially if there can be Higher Vampires that can bear children despite the species being all male usually. Maybe those vampires even have a specific pronoun, just for them! The vampire language shown in the games is mostly derived from Etruscan, (an ancient language that we only know for certain the meanings of a few hundred words) which (to my minimal knowledge of how languages work, and a few Wikipedia articles) seems to only have two pronouns.
Anyway, this is my worldbuilding of the Witcher vampires, but feel free to ask me to clarify if something is a bit muddled, use this worldbuilding in your own stories, heavily adapt it, or correct a fact I got wrong! I really enjoy people using little pieces of my ideas! I'm hoping to post a little more often in the future, but I can't promise anything. I should respond to comments/people tagging me more often now though!