From Nabokov's Speak, Memory:
"The mysteries of mimicry had a special attraction for me. Its phenomena showed an artistic perfection usually associated with man-wrought things. Consider the imitation of oozing poison by bubblelike macules on a wing (complete with pseudo-refraction) or by glossy yellow knobs on a chrysalis ("Don't eat me--I have already been squashed, sampled and rejected"). Consider the tricks of an acrobatic caterpillar (of the Lobster Moth) which in infancy looks like bird's dung, but after molting develops scrabbly hymenopteroid appendages and baroque characteristics, allowing the extraordinary fellow to play two parts at once (like the actor in Oriental shows who becomes a pair of intertwisted wrestlers): that of a writhing larva and that of a big ant seemingly harrowing it. When a certain moth resembles a certain wasp in shape and color, it also walks and moves its antennae in a waspish, unmothlike manner. When a butterfly has to look like a leaf, not only are all the details of a leaf beautifully rendered but markings mimicking grub-bored holes are generously thrown in. "Natural Selection," in the Darwinian sense, could not explain the miraculous coincidence of imitative aspect and imitative behavior, nor could one appeal to the theory of "the struggle for life" when a protective device was carried to a point of mimetic subtlety, exuberance, and luxury far in excess of a predator's power of appreciation. I discovered in nature the nonutilitarian delights that I sought in art. Both were a form of magic, both were a game of intricate enchantment and deception."
My students, I was happy to see, were a little shocked that someone with Nabokov's way of seeing things would say something that might even remotely be construed as Intelligent Design-ish. And indeed, Darwinian natural selection, as I understand it, does have a fine explanation for the "miraculous coincidence of imitative aspect and imitative behavior": any mutant variety that doesn't exhibit a perfect imitation is going to get eaten. And if you have enough random-pattern butterflies getting eaten over time, eventually a strain that has a slightly better design is going to come around and not get eaten.
I tried to deflect the conversation onto his real substantive point here, which is that for Nabokov art requires a kind of heroic, almost obsessive attention to mimesis. You put way more effort into representing the world in your art than your predator (or reader) is likely to ever notice. The art comes from the excess, which is, like the butterfly that looks like a leaf with "grub-bored holes," also always in some sense deceptive ("an intricate enchantment and deception"). If art is both mimetic and deceptive, perhaps Nabokov is trying to say that mimesis itself is always deceptive. You make a butterfly that looks amazingly like a leaf, but you don't attempt to clone the genetic structure of the leaf itself. Indeed, in some sense you don't care about the leaf per se (i.e., reality) at all.