It’s actually called hemolymph, but it looks like human blood.
I’ve scoured the Internet and library and haven’t found much information on the process of butterfly wings drying. Well, there’s some, but it’s all about the hemolymph pumping through the wings as they unfurl during metamorphosis. I found it far more interesting, and somewhat puzzling, to watch them drip dry red.
The puzzling part was the color of the hemolymph. The drops on the newspaper were clearly red, but here’s a drop on the wing:
Oxygen is the only logical explanation; I found that butterfly hemolymph is normally the color seen in the latter shot. This is a definition for hemolymph from The Lepidopterists’ Society:
Hemolymph: The typically yellowish colored fluid that carries nutrients (though not oxygen) around the body of the butterfly; the lepidopteran version of “blood”.
After four missed metamorphoses, I feel lucky to have a caught a glimpse of the golden hemolymph before the oxygen seeped in!