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Why do vampires suck only a liitle blood out of their human prey and not drink all the blood available in the human's body (or store the blood for future use)?

In the movie, when the bad vampires were forming their army, they drank only a little blood out of each human.

  • The vampires in THe Saga of Darren Shan do this to avoid having angry mobs come after them with pitchforks (according to Larten Crepsley in the movie). They drink from the shoulders of humans, and they do this to avert the stupid claim that you have to kill when you feed on humans. The vampaneze, however, drain humans completely and take on their spirits inside of them after they die. The vampires do this only if their targets die from other causes, such as Darren drinking Sam Grest's blood after the Wolf Man ate him. – karen stickney Oct 7 '16 at 20:39
  • This doesn't explain why they do this in twilight – Valorum Oct 7 '16 at 21:14
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In Breaking Dawn (I think) we learn that it is the human blood in a newborn that fuels their increased strength and speed - so much human blood in their bodies makes them more powerful, and no older vampire can compare (they are limited to what they can hold in their stomachs, newborns use their whole bodies).

It's likely that they drank as little as possible so the newborn's strength would be as high as possible and last for as long as possible.

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I think this question is based on a false premise. I am reasonably sure that vampires from the Twilight series who feed on human blood routinely drink as much of it as they can easily get out of the body.

When changing a human to a vampire, in the Twilight books, it is not necessary to drink any blood at all. One bite that injects even a tiny amount of venom is all that is necessary.

  • In the movie, when the bad vampires were forming their army, they drank only little blood out of each human. – user5421 May 6 '12 at 5:44
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    They probably only drank a little because they were making an army, and didn't want to kill the human before it was turned. – Zoe May 6 '12 at 5:45
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In the books, vampires completely drain their prey (human or animal) of blood when feeding, or at least as much as they can get. The times when a human isn't sucked completely dry are usually when the vampire is interrupted in their feeding (as in Carlisle's case; also, most of the scenes of the newborn army in Eclipse involve newborns breaking away from feeding to fight their fellow newborns), the vampire is trying to turn and not feed on their victim (numerous examples), or the vampire is simply trying to kill (Rosalie, killing her former assailants after she was turned).

To turn a vampire in the Twilight universe, you cannot drain them dry (unlike many other universes where draining and then an exchange of blood is required). So, when you're actually trying to create a new vampire, you just have to bite, but then you have to control your thirst and not feed on the human you're turning. Of course, draining a LITTLE blood is OK.

When a vampire really is interested in feeding, understand that a cut to the neck (or any major artery) only produces blood as long as the body continues to pump it, thus producing blood pressure. Once the heart stops and the blood volume is no longer "stretching" the arteries and veins, the bleeding would stop, and it's rather difficult to "suck" blood out of a body through any extremity's artery including the carotid. Only gravity would continue to produce blood from the puncture, and we don't typically see vampires stringing their prey upside down to let the remaining blood drain. So, a "drained" victim (no longer pumping blood into the vampire's mouth) can still bleed after being discarded.

Also, from an out-of-universe perspective, any demonstrated "wastefulness" on a vampire's part simply increases the horror factor. Not only is there more blood to show pumping out of neck wounds, but the victim is often still alive, and the vampire often tosses one victim aside to sink their teeth into another. As the Twilight films are PG-13 there's a cap on the amount of gratuitous blood that can be shown, but you can still have a little fun.

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Four generic points can help answer this.

  1. Not knowing the exact amount of change a Twilight vampire goes through, we only have human standards to compare to. The average human stomach can only hold 1.5 Liters of liquid at any given time. The average human body has ~5 Liters of Blood. Blood donation is typically limited to 1 Pint (.47 Liters) and many people feel woozy/faint even donating that much. Losing 40% of your blood puts you in fatal danger without immediate emergency response. That's 2 Liters for a 5 Liter body. 1.5 Liters, or 3 Pints, can lead to shock and death in many people. So, a hungry vampire, taking a full stomach's amount of blood, can leave a person 70% full of blood and still in very dangerous medical condition.

  2. In a lot of vampire lore, blood isn't just about the physical properties of blood. Blood is life, is magic. Stale or spoiled blood doesn't have the thing that they really require. Anne Rice's vampires can't drink the last drops of blood from a person without dying themselves. Or just like regular food, it goes bad, even with storage. Some stories show that simply raiding blood banks doesn't work (while other stories do), so they create human farms like in Blade 3.

  3. Vampires don't care enough about people to think of their food source as precious or worth stockpiling (instead of stockpiling humans). They are just straight evil and have no problem killing another human next time they are hungry. It's similar to how some people will go fishing, catch a big fish, eat half, throw the rest away, then go fishing again.

  4. As for the army part, Twilight vampirism only requires that their venom be injected into a human. Biting is just a convenient method of transmission, but I'd assume spitting (they don't have saliva, it's also venom, as are their tears and other bodily fluids) into an open wound or with a needle or anything (except sex, for some not-explained and probably ridiculously hand-waved reason). They wanted an army, not a feast. So they bit a human, bit back the urge to suck them dry and waited for the venom to transform the human into a vampire. It was a conscious choice not to feed. Not that we saw much of the typical vampire feeding in Twilight like we see in other movies.