Thursday, December 18, 2014

Biology of Blood-Drinkers

From the author's note in a recent vampire novel, I discovered a book that would be fascinating and valuable to all writers who create vampires as well as anybody interested in the often "alien" weirdness of animal biology and behavior in our terrestrial ecosystems. DARK BANQUET (2008), by bat expert Bill Schutt, subtitled "Blood and the Curious Lives of Blood-Feeding Creatures," surveys the "obligate sanguivores" (creatures that feed exclusively on blood) of the animal kingdom. The animals discussed range from vampire bats (the only mammal in this category) to leeches, bedbugs, ticks, etc., with glances at a few creatures that sometimes consume blood but don't live on it, such as "vampire finches." Anticoagulants and anesthetics in the saliva of vampire bats and leeches have inspired similar features of the naturally evolved vampire species in my own fiction. It's intriguing that, because of the high volume of water to nutrients (mainly protein) in blood, vampire bats have to ingest a large percentage of their body weight every day, yet leeches and bedbugs can go for weeks or months without feeding. What makes the difference—the metabolic rate of mammals versus invertebrates? If so, my own vampires' ability to survive in a dormant state, without nourishment, theoretically forever must be a bit of a hand-wave, but after all, it's fiction. I've also postulated that my vampires' saliva has antiseptic properties that keep the bite wounds from getting infected; the saliva of human beings and some other animals does contain antibacterial chemicals, but this book doesn't mention any such qualities in bats or leeches.

One vampire bat trait I definitely did not adopt for my fictional species is the need to get rid of excess water to make themselves light enough to fly away after drinking from a victim. The bats often start urinating even while they're still feeding. Far from glamorous!

After the opening chapter on vampire bats, enlivened (like the rest of the book) with personal anecdotes and observations, Schutt devotes a section to the physiology and chemistry of blood in the context of the history of medical science. One topic I wish he'd covered more thoroughly, instead of briefly mentioning, is the nutritional content of blood and the digestive adaptations needed for an animal to survive on what his final chapter labels "A Tough Way to Make a Living." I've often wondered how many calories are in a pint of blood and have never been able to find a definitive answer.

For me, the most fascinating tidbit of information in the book is that vampire bats have been observed to snuggle up to the brood patches on hens' chests. The hen relaxes, contentedly settling down as if the predator is a chick, and allows the bat to feed. On other occasions, a hen may respond to a bat on her back by passively assuming the mating posture, as if mounted by a rooster. So my premise that members of my vampire species lull or seduce human victims into willingly surrendering their lifeblood has a factual basis in biology!

Margaret L. Carter

Carter's Crypt


  1. Fabulous information, Margaret. If you don't go into urination, I don't suppose you go into defecation, either, but.... from your expert point of view, do vampires poop?

    Sorry to be coarse, but I am participating in a ConFusion workshop on fantastical pooping, and would very much appreciate input.


  2. That sounds like a unique panel! My vampires do both, because they're a naturally evolved species, not supernatural. I postulate that they have a more efficient physiology than we do, so they eliminate less frequently than human beings, not more. Also, during their periods of daylight dormancy, near-deathlike sleep, all bodily functions are suspended except the minimal respiration and circulation to keep them alive. (Sunlight doesn't kill them, only makes them uncomfortable or sick, and they don't HAVE to sleep all day, but they prefer to if possible.) As for the traditional supernatural vampires, the usual fictional convention seems to be that all the blood they ingest is magically fully absorbed, so there's no elimination.

  3. rowena cherry4:35 PM EST

    Thank you, Margaret. :-)

  4. I HAVE run across a different approach to the supernatural vampire: A few authors postulate that a vampire weeps, sweats, and urinates blood. Bloody tears, particularly, are not uncommon. (Solid waste is never mentioned; the assumption seems to be that there isn't any.) A healthy naturally evolved vampire wouldn't urinate blood, since blood in the urine is a sign of injury or disease. Anne Rice, as you probably recall, has her newly created vampires void all their body's human waste products through every orifice; after the transformation is complete, there won't be any waste products.