Butterflies are metal af

The pokémon Vivillon is a butterfly and in the pokédex it's number is #666

Not sure on the "can or will drink blood" issue. But I do know that butterflies often collect sodium salts as part of their mating ritual. Perhaps the blood thing is related?

I've heard that they sometimes swarm the eyes of animals, making them cry, then drinking the tears.

That's so Metal!
"YESSSS... Your sadness nourishes me."