Biologists have long assumed that proboscis-bearing butterflies and moths like those of today (those of the Glossata clade) evolved to feed on and pollinate flowers, therefore that flowers evolved first and that butterflies evolved their siphoning-sucking proboscis late so as to better take advantage of their abundant nectar.
However, rock samples dating back to about 200 million years ago and collected from northern Germany in 2012 by paleontologists Paul K. Strother of Boston College and Bas van de Schootbrugge of the University of Utrecht, with undergraduate student Timo J. B. van Eldijk doing the grunt work of analyzing them, revealed fossils of tiny hollow scales that looked a lot like the scales found on modern butterfly wings.
They called in Torsten Wappler, a University of Bonn scientist specializing in extinct insects and he confirmed their suspicions. Those 200 million-year-old scales did indeed belong to butterflies of the proboscis-bearing type (the more primitive butterflies with chewing mouthparts had solid scales). Yet that’s 70 million years before the first insect-pollinated flowers appeared.
Something was wrong with the theory. It would appear that the butterfly proboscis evolved before the first flowering plants.
This has led to a new theory: that butterflies developed their proboscis to feed on something else, then, when flowering plants came along, were able to quickly adapt to the new food source. But what were these first modern butterflies feeding on?
The researchers suggest pollination drops. These are secreted by the female flowers of gymnosperms (conifers) so the wind-borne pollen from male flowers has a place to stick to. Would it not be likely that butterflies first developed a proboscis to suck up the sugary pollination drops and its associated pollen, a highly interesting food source, then switched to the even more abundant nectar reward of angiosperm flowers when they came along 70 million years later?
Of course, this remains only a theory, but an intriguing one. What is clear, though, is that the butterfly came along long before the first nectar-bearing flower appeared.
You can read more about the study that came to this fascinating theory here: A Triassic-Jurassic window into the evolution of Lepidoptera.