[Henry Walter] Bates explained to [Charles] Darwin that he had found [in Brazil] many instances in which a completely harmless and potentially edible animal resembled a distasteful, inedible, noxious or poisonous species. He observed flies that looked like bees, beetles that looked like wasps, even caterpillars that looked like pit vipers. He referred to these as “analogous resemblances” or “mimetic analogies.”Some people are amazed by this kind of mimicry (insect mimicry); others, such as myself, are deeply unsettled by it. How much of it is intentional? Most likely none of it is—meaning, it's not even mimicry. But how is it possible that mere accidents can, say, make a fly look like a bee? How? And yet that is how it happened. One has to give up and feel the trouble in the soul, the trouble in the world.
Bates deduced that defenseless mimics gained an advantage by resembling well-defended species. He concluded that the many cases he had observed were not mere coincidences, as the mimicking forms only occurred in the same geographical area as the species they imitated. He offered the phenomenon, still referred to today as Batesian mimicry, as “a most beautiful proof of the theory of natural selection.”
Some less scientific, more sentimental naturalists of the day were inclined to view these resemblances among species as merely nature’s proclivity for beauty and ornamentation, not the consequence of the battle of nature. Bates countered by pointing to other kinds of imitations, like moths and caterpillars that resembled bird droppings.