Bruce looks up from the book he’s been reading —something boring Tony doesn't even bother looking at— and raises a brow. “Yeah, I've got you. Which ones?”

Tony waves a hand from the comforter without lifting his head. “Dealer’s choice. Moths or something. I don’t really care. Make it boring enough to knock me out.”

Bruce snorts, sets the book aside, and thinks for a moment. “Actias selene,” he says finally, voice low and even.

Tony rolls onto his side, eyes half-open. “Gesundheit.”

“It’s an Indian moon moth,” Bruce explains, undeterred. “One of the larger silk moths. Wingspan’s about—” he holds his hands apart, “—four to seven inches, give or take. Pale green, with these little eyespots that make them look like they’re glowing in moonlight.”

“Mm,” Tony hums, eyes already starting to droop.

“They only live for a week after they emerge,” Bruce continues softly. “They don’t even have mouths. Their whole life as an adult is just… finding a mate, laying eggs, and then they’re done. Everything they need to survive, they built up as a caterpillar.”

Tony mumbles something that sounds like “that’s depressing,” but his voice is already fading.

Bruce smiles faintly. “I don’t think so. They spend all that time preparing for this one short, perfect moment. It's kinda beautiful.”

He glances over at Tony. Dead asleep. His breathing has evened out, one arm curled under the pillow.

Bruce shakes his head, amused, and reaches over to pull the blanket over him, just enough to keep him from getting cold.