There are a number of similarities that can be made between bedbugs and vampires.
The obvious one is, of course, the fact that they are both active only at night. As the sun sets and you slip into a deep, dreamless sleep, a vampire emerges from the shadows and stands silently at your helpless, unconscious form. You cannot see the vampire. Even if you were awake, the vampire would not want you to. Similarly, and simultaneously, a bed bug emerges from the dark folds of your used mattress. It ponders your skin. It creeps soundlessly around you, until it stops.
Both the bedbug and the vampire see you as their prey. Their perception is accurate.
In the case of both creatures, the lore that is associated with them is often difficult and contradictory. Can a vampire be killed with a wooden stake, or do you have to set it on fire? Can you use a bug bomb to save yourself, or do you have to call a professional fumigator? Is it possible to sleep with your mattress encased in plastic while you wear a chain of garlic around your neck - and will either of these things actually protect you?
The short answer is that there is no answer. The only answer is possibly. Rituals, in their many and complex variations, are never guaranteed to be successful. This is as true in black magic as it is in insect extermination.
Returning to your bed, both the bedbug and the vampire are feeding. Blood is, of course, life. Your life. And at present, it is being drained from your body to feed the life of another.
Routine is important. The vampire drinks from the same place on your body it always has. It will return to this place - your neck - over, and over, and over again, never straying from this fixed place. It is both practical and a compulsion. Vampires are, by nature, compulsive beings. They have a long, ancient history with obsession - obsession with numbers, with counting, with practice.
Bedbugs are similar. In the morning you will wake up covered in red marks. You will notice that these marks tend to cluster. There is never only one. Once the bedbugs have learned how your blood travels through your body, they will find a place and feed again, and again, and again. The marks they leave will pile onto you, change you - the layers of enflamed sores distorting the familiar topography of your skin.
What happens next varies in both cases. The sun will rise. The bedbugs and the vampire will retreat into the shadows, quenched. You will wake up and somehow things will be different. You may itch in places you did not itch before. You may be lightheaded, pale, with a thirst for something you can't entirely put into words. You may not even be human. Or, at the very least, you may not feel like you are.
I should mention that I have it under relatively good authority that my apartment is, in fact, infested with bedbugs and not vampires. But you can never really be sure, can you? Tomorrow I could begin the last year of my undergraduate education as an entirely different being. Either way, I will certainly be an itchier one.