Good Heavens what insect can suck it'- Charles Darwin, Angraecum sesquipedale and Xanthopan morganii praedicta

Abstract

In this review we provide a detailed description of Darwin's prediction of the coevolution of a long-spurred orchid, Angraecum sesquipedale, and a long-tongued moth, his correspondence on the subject, the history of the moth and the subsequent literature. On seeing the long spur of A.sesquipedale, Darwin predicted that its pollinator would be a moth with a long proboscis. For more than a century following Darwin's prediction this was assumed to be the case. The pollinator was taken to be Xanthopan morganii praedicta, despite the fact that it had not been observed to visit A.sesquipedale flowers. Direct observations, infra-red cinematography and photographs published between 1993 and 1997 and a video made in 2004, all of which show X.morganii praedicta visiting A.sesquipedale flowers and removing pollinia, proved that Darwin's prediction was accurate. Recent research suggests that selection pressure exerted by predators on the pollinators, resulted in the evolution of extreme tongue lengths and a special hovering flight. © 2012 The Linnean Society of London.