How Do Vampires Eat? Depends...

Between substitute teaching in a high school (at the time the movie Twilight hit the screen) and doing National Novel Writing Month, I've been exposed to a lot of chatter about vampires lately. I think the movie's number one at the box office this week and it seemed as if something like half the NaNoWriMo books involved them in one form or another. People seem to have a romantic attachment to the old bloodsuckers (oddly enough, they don't have the same attachment to leeches, which are arguably more useful than the undead).

I've never been quite as enamored of vampires as characters. For one thing, the physics always baffled me: how can a 150-pound human turn into a 200-pound wolf and then into a three-ounce bat? There's this little thing called the law of conservation of mass. Well, Andrew Fox dealt with this question in his most entertaining book Fat White Vampire Blues. I'm not going to give away the secret, but I will say it's a very satisfying resolution of the physics question.

But now, courtesy of NPR's Science Friday show, we've got a new problem in vampire engineering: fluid flow. According to biology professor and author Bill Schutt, blood is a pretty thin soup--almost entirely water, with a little bit of salt and protein, and no fat at all. Which means that vampire bats (and other creatures that live on blood) have to consume a lot of it. Which in turn means they have to get rid of a lot of water--if Dracula empties his victim's veins, he's going to ingest a gallon of water, which is about four times what an average person excretes in a day. No kidney stones for the undead, I guess, but a major disposal problem. According to Schutt, vampire bats solve this problem by simultaneously feeding and peeing. Well, doesn't that add a little something to the romantic vampire mystique?

However, I've never seen a vampire movie (or read a vampire book) in which the undead unzip before dining, so the question arises: do vampires just possess the world's largest bladders? Or are they all secretly going around in those NASA diapers, the ones that hold a full day's worth of urine?

The answer to that question is, of course... depends.