Arditti, J., Elliott, J., Kitching I.J. and Wasserthal, L.T. (2012): ‘Good Heavens what insect can suck it’ – Charles Darwin, Angraecum sesquipedale and Xanthopan morganii praedicta. Botanical Journal of the Linnean Society, 169, 403–432.

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, Botanical Journal of the Linnean Society, 2012, 169, 403–432.

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Figure 6. Xanthopan morganii praedicta from Madagascar. A, male of 5th generation bred in captivity, viewed from below. Underside of abdomen is pinkish whereas the underside of moths of the other subspecies from Africa (Fig. 7D, E) is white. B, same male viewed from above. Coloration, wing patterns and morphology are similar to moths from Gabon, Africa (Fig. 7). C, female of 5th generation bred in captivity. D, larger male from the wild. E, lateral view of head with proboscis and spiny labial palps of a male. Scale bars = 10 cm (L. T. Wasserthal). F, coiled long proboscis of a Brazilian moth (Müller, 1873).