You may be perusing Literotica or another [lesser] erotica website. You may find a new lesbian erotica tale that you start reading. And you may say to yourself, hmm, this lesbian erotica seems odd, but I can't quite put my finger on it. Allow me to assist, Fearless Reader. For in fact, you are not reading lesbian erotica -- you're reading vampire erotica. In these stories, lesbianism is portrayed as something that can be spread like the fucking plague, or, like, you know ... vampirism.
Now, can lesbians be vampires, and vice versa? Of course. In fact, there's a whole subgenre built around precisely that. But there are also stories out there that seem to want you to believe that they're lesbian tales set in the real world, where in fact the real world is nowhere in sight, stories that only make sense if you accept supernatural elements in them, but that never admit being supernatural stories.
Some points to consider, if you will:
1. The initial sexual encounter almost always involves a heterosexual woman ("straight") who has never had sex with another woman before. The encounter is almost always portrayed as an initiation in which the straight woman is docile and/or submissive.
2. The initiating homosexual woman (the seducer) is almost always dominant and older.
Now, you may be saying to yourself, "But caleb35, those aren't necessarily attributes of a vampire story," and you'd be correct. God only knows, I've dabbled in these tropes myself (though I'd claim that I'm more interested in older-younger, power dynamics, and the lesbian as Other, rather than vampirism per se, but that's a discussion for another time with my therapist). And if the points above are on their own, I'd say maybe you're right. It's when those points are combined with the ones below that you're on your way to Vampire Town: