Rounding a curve in a trail in Magnuson Park, I noticed a pair of withered willow leaves that seemed strangely symmetrical. On closer inspection, they weren't leaves at all.

They were the wings of a sphinx moth. A biiig sphinx moth.

That's my not-especially-big thumb. I figure the fore-wing of this beastie measures five centimeters. Looks to me like a Smerinthus opthalmica, a lumbering nocturnal moth whose caterpillars feed on willow and cottonwood. The adults don't feed on anything. They don't have the mouth parts. They are just around to make caterpillars.
S. opthalmica aren't the only monster moths haunting our nights hereabouts. There are other sphinx moths, and giant silkworm moths including the gloriously named Polyphemus.
Here's another angle on the creature.