"In one famous case, putting the final QED on Darwin's proof that evolution had tailored a flower to lure and exploit a specific pollinator had to wait a few decades. Attempting to explain why the star orchid of Madagascar would secrete a drop of nectar at the tail end of a foot-long floral spur, where no known pollinator could possibly get at it, Darwin hypothesized the existence of a moth with a 12-inch-long tongue, an unlikely creature that had never been observed. Vindication arrived a couple decades after Darwin's death, when entomologists unfurled the tongue of a newly discovered hawk moth and found that it measured nearly a foot long."
Love & Lies, Michael Pollan (with Christian Ziegler), National Geographic, September 2009, pp. 100 - 121.I find this snippet from Pollan's article the most beautiful among the numerous examples he cites from the diverse and extremely specialised bag of tricks orchids have evolved to fool insects into pollinating them. Scarcely can one desist from asking why an orchid exhibits some extremely complex feature, even if the answer is: "the feature was chanced upon quite at random, but by exhibiting it the orchid is today alive!"
The orchid in question, Angraecum sesquipedale ("Darwin's
orchid"), and also the hawk moth, Xanthopan morgani ("Darwin's Hawk
Moth"), have their own pages on Wikipedia:
http://en.wikipedia.org/wiki/Angraecum_sesquipedale
http://en.wikipedia.org/wiki/Xanthopan_morgani
Gene Kritsky's article, Darwin's Madagascan Hawk Moth Prediction, provides a wonderful account of the late 19th-century tussle that Darwin's prediction of the existence of a hitherto unsighted moth unleashed between believers on non-believers of evolution. The moth was only sighted after Darwin's death; fittingly, it was named Xanthopan morgani praedicta!