OK, here's an idle thought (and a question) for you ...
A couple of weeks ago at the British Eastercon I found myself on a panel discussion about vampires. (Hey, I've been trying to get the hell away from being Mr Singularity Guy for years now; what's your problem?)
Anyway, there I was sitting with Freda Warrington and Jim Butcher, and our moderator opens up by asking, "what makes vampires sexy?"
And I suddenly realized I had come to the right place for an argument. Because ...
Vampires are not sexy. At least, not in the real world.
Desmodus rotundis isn't sexy. (Except insofar as small furry rodents that carry rabies aren't as un-sexy as some other obligate haemophages.) Bed bugs are really not sexy. But if you want maximally not-sexy, it's hard to top Placobdelloides jaegerskioeldi, the Hippo Arse Leech.
The Hippo Arse Leech is a leech; it sucks blood. Like most leeches, its mouth parts aren't really up to drilling through the armour-tough skin of a hippopotamus, so it seeks out an exposed surface with a much more porous barrier separating it from the juicy red stuff: the lining of the hippo rectum. When arse leeches find somewhere to feed, in due course happy fun times ensue—for hermaphrodite values of happy fun times that involve traumatic insemination. Once pregnant, the leeches allow themselves to be expelled by the hippo (it's noteworthy that hippopotami spin their tails when they defecate, to sling the crap as far away as possible—possibly because the leeches itch—we're into self-propelled-hemorrhoids-with-teeth territory here), whereupon in the due fullness of time they find another hippo, force their way through it's arse crack, and find somewhere to chow down. Oh, did I mention that this delightful critter nurtures its young? Yep, the mother feeds her brood until they're mature enough to find a hippo of their own. (Guess what she feeds them with.)
Here 's a video by Mark Siddall, professor of invertebrate zoology at the American Natural History Museum, a noted expert on leeches, describing how he discovered P. Jaegerskioeldi, just in case you think I'm making this up.
By the end of my description Jim and Freda were both ... well, I wish I'd thought to photograph their faces for posterity. So were the audience. And that's when I got to the money shot: the thing about fictional vampires is, vampires are only sexy when they're anthropomorphic.
Let's leave aside the whole living dead angle (a callback to ancient burial traditions in northern climes, where the decay of corpses might be retarded by cold weather: and when a family sickened and died one after the other, from contagious diseases such as tuberculosis, on opening the family crypt an undecaying rosy-cheeked corpse might be found with blood trickling from its mouth). Let's look solely at the vampire motif in modern fiction, where sexy vampires are used as a metaphor for the forbidden lover. Do we see anything approximating a realistic portrayal of actual blood-drinking organisms? Do we hell! Blood isn't actually very nutritious, so haemophagous parasites tend to be small, specialized, and horrifyingly adapted: biological syringes with a guidance system and a digestive tract attached. If we expanded a real one to human size it'd be a thing of horror, fit to give Ridley Scott or H. R. Giger nightmares. But I digress: the thing is, we know what real bloodsucking fiends look like, and do we find them in our fiction? We do not.
So here we have a seeming paradox: a class of organism that is represented in fictionalized, supernatural form in a manner that is pretty much the antithesis of their real world presentation. There's an entire sub-genre in which we are expected to temporarily pretend that the smouldering sexy vampire lover isn't actually a hippo arse leech squirming and eager to dig it's jaws into your rectal mucosa. And now I am shaking my head and wondering, thoughtfully, if I can see any other parasitic life-cycles that are amenable to converting into supernatural fictional tropes? (Your first example being, of course, my use of angler fish sex as a model for unicorns ...)
PS: If you are a creationist, the onus is on you to come to terms with why your God saw fit to inflict a parasite like this on hippopotami. Just sayin'.