Wasserthal, L.T. (2013): Evolution of long-tongued hawkmoths and pollination of long-spurred Angraecum orchids. Proceedings of the 20th World Orchid Conference, Singapore 2011, 280-284.
Since Darwin the extremely long tongues of tropical hawkmoths have been interpreted to be the result of a coevolutionary race with long nectar spurs of orchids. However, extremely long-proboscis hawkmoths are not restricted to the exploitation of highly specialized sphingophilous flowers. Due to their long tongues and a swing-hovering flight they avoid ambush predators such as huntsman spiders, which lurk among flowers. However, swing-hovering hinders full insertion of the proboscis into the long spurs of orchids. Some orchids prevent the moths from the swinging flight by forcing them to land on their protruding labellum. This is the case with Angraecum sesquipedale and Xanthopan morganii praedicta . Illegitimate visitors with tongues longer than the orchid spurs can exploit the nectar or even waste the pollinaria, thus exerting selection pressure towards spur elongation with the consequence of pollinator-shift from shorter- to longer-tongued moths.
Fig. 1. A Cupiennius coccineus spider changes from lurk (a) to attack position (b) without jumping at the hovering Agrius cingulatus moth, which is swinging in front of an artificial blossom between position (a) and (b). From Wasserthal (2001).
Fig. 4. (a) Two Xanthopan morganii praedicta swing-hovering in front of Angraecum longicalcar without an attemptto fully introduce extended tongues into the spur. The moths did not obtain access to the nectar column and did not remove the pollinaria. (b) An unusual not spontaneously swing-hovering female Coelonia solani removed and transferred the pollinaria at the base of the proboscis (arrowhead). This is the first documentation of a successful visit to Angraecum longicalcar by an extremely long-tongued hawkmoth.