This was going to be a short rant. It got away from me a bit more than I wanted, but oh well.
There's been many a lovely and thoughtful rant about how women in fiction never seem to menstruate. Okay. Problem acknowledged.
Now, let's take this a step further, and add vampires to the mix. Now, vampires can be the subject of a whole other rant, re: their portrayals, but I'm going to keep this nice and simple.
There are a lot of vampires out there with heightened senses of smell. They're able to smell the blood pumping through human veins, and oh, it is a source of torment. Oh, it signals their prey. Good vampires or evil vampires, they all can OMG SMELL THE BLOOD, with a very few exceptions.
How does menstruation affect this? There's a human, right there, bleeding. Logically, quite a few things should be able to smell the menstruation, but vampires especially. And yet, the subject is conveniently ignored in all the fiction I've read, save for one Anne Rice novel, in which Lestat goes down on a menstruating nun.
I call bullshit. Especially if there are tormented, blood-smelling vampires.
How does it affect them? Remember that, in most cases, this won't be fresh blood. This is blood and uterine lining and mucus, and it's being expelled as waste... Which isn't what the OMG MENSTRUAL BLOOD IS MAGICALLY POWERFUL AND A SIGN OF YOUR CONNECTION TO THE GODDESS crowd really wants to hear, but... That's what it is. Bodily waste. Not to say that it isn't powerful, but then, if your nature-based spirituality is logical, so is taking a good shit. Returning nutrients to nature, huzzah! Human fertilizer! The Circle of Life!
Any special power inherent in menstrual blood lies in its symbolism -- it represents female fertility. Symbolism is awesome and powerful, but there is no inherent awesomeness in the biological makeup of the blood itself. Bodily waste, people. On a biological level, it's like taking a prolonged shit that can last up to a week.
So how would a blood-devouring species deal with it? Is it a poor substitute for fresh, living blood, not as nourishing, but edible in a pinch? Is it repellent to them? I'd imagine being able to smell the decaying blood as it's expelled would be, for a vampire, the equivalent of leaving a piece of meat on the counter for a few days -- not so bad at first, but after a while, you just don't want to be around the smell of rotting food.
And it'll depend on the woman's menstrual cycle. Do they bleed out heavily and quickly, with one day of strong, red blood and then taper off into brown stuff? Or is it brown and icky right from the start, stretching out for a while? If there's a quick expulsion of relatively fresh blood, your average vampire might react differently to that than they would to dribbles of rotting brown blood and tissue.
Maybe when the bleeding starts, J. Random Vampire is ready to dive right in, but on the second and third day, se's quite interested in finding somewhere else to be. Maybe the smell of menstruation isn't so bad by itself, but it only serves to highlight the fact that there's all this lovely fresh blood in reach.
In most fantasy fiction -- hell, most fiction in general -- menstruation is either ignored or romanticized. To be honest, neither approach does anything for me. I don't expect periods to be rendered in loving detail, much like I don't need to know every time a character takes a shit (though if a character never visits the bathroom/privy/whatever, I'm also inclined to be a bit suspicious, especially when a character's day is otherwise rendered in obsessive detail). On the other hand, for all that I understand the urge some Neopagan/feminist-leaning authors have to not say anything negative about sacred moon-time or whatever... Quite a few women get cramps. Some of them get bitchy, or weepy. It's not always a lovely, sacred thing, or an easily ignorable thing.
For instance, I never thought the emotional aspects of PMS applied to me, ("Yeah, yeah, cramps will make anyone feel crappy, but I'm not some hormone-fueled psycho!") until I realized that a few days before my period, I always had a horrible emotional meltdown for one reason or another. Every. Single. Time. It's not universal -- it's not even common -- but it happens.
Humans who are born female tend to menstruate. Taking hormones (whether for birth control or gender reassignment) can change that. Diet and activity levels can change that. And of course, there's menopause. But not every woman is immune to bleeding from the crotch once a month simply by virtue of being fictional. It shouldn't have to be a big deal, or the focus of a story, but somewhere, at some point, it is happening, and it will affect things. Just give me some indication that you've considered it, people. Please.
(I was just pointed at
Ginger Snaps as a treatment of the subject with werewolves. Awesome. I must see this movie.)