|Natural History Museum of London|
Rothschild & Jordan, 1903
Xanthopan is a monotypic genus of sphinx moth, with Xanthopan morganii (commonly misspelled as "morgani"), or Morgan's sphinx moth as its sole species. It is a very large sphinx moth from East Africa (Rhodesia, Nyasaland) and Madagascar. Little is known of the biology, though the adults have been found to visit orchids (see below).
In January 1862 while researching insect pollination of orchids, Charles Darwin received a package of orchids from the distinguished horticulturist James Bateman, and in a follow up letter with a second package Bateman's son Robert confirmed the names of the specimens, including Angraecum sesquipedale from Madagascar. Darwin was surprised at the defining characteristic of this species: the "astonishing length" of the whip-like green spur forming the nectary of each flower, and remarked to Joseph Hooker "I have just received such a Box full from Mr Bateman with the astounding Angræcum sesquipedalia with a nectary a foot long— Good Heavens what insect can suck it"[?] The spur of the flower is 20–35 cm (7.9–13.8 in) from its tip to the tip of the flower's lip. The name "sesquipedale" is Latin for "one and a half feet," referring to the spur length.
From his observations and experiments with pushing a probe into the spur of the flower, Darwin surmised in his 1862 book Fertilisation of Orchids that there must be a pollinator moth with a proboscis long enough to reach the nectar at the end of the spur. In its attempt to get the nectar at the end of the spur the moth would get pollen rubbed off on its head. The next orchid it visited would then be pollinated in the same manner.
In 1867 Alfred Russel Wallace published an article in which he supported Darwin's hypothesis, remarking that the African sphinx moth Xanthopan morganii (then known as Macrosila morganii) had a proboscis almost long enough to reach the bottom of the spur. In a footnote to this article Wallace wrote "That such a moth exists in Madagascar may be safely predicted; and naturalists who visit that island should search for it with as much confidence as astronomers searched for the planet Neptune,--and they will be equally successful!"
Subsequently, specimens of Xanthopan morganii (commonly called Morgan's sphinx moth) with an especially long proboscis were collected in Madagascar. Since Wallace predicted that the mystery pollinator would turn out to be a sphinx moth, rather than simply a large moth as Darwin had suggested, the Malagasy form was named subspecies praedicta by Walter Rothschild & Karl Jordan in honor of Wallace's (not Darwin's) prediction. Darwin's earlier, but less specific, prediction was not even mentioned by Rothschild and Jordan. The description of Xanthopan morgani praedicta, as a sub-species of the African hawk moth was later determined to be invalid (it is identical to the mainland form of the species).
Morgan's sphinx moth approaches the flower to ascertain by scent whether or not it is the correct orchid species. Then the moth backs up over a foot and unrolls its proboscis, then flies forward, inserting it into the orchid's spur.
- Walker, F. (1856). List of the Specimens of Lepidopterous Insects in the Collection of the British Museum 8: 206
- Kritsky, Gene (1991). "Darwin's Madagascan Hawk Moth prediction" (PDF). American Entomologist. 37. pp. 206–9. Archived from the original (PDF) on February 29, 2012. Retrieved 2009-02-09.
- "Darwin Correspondence Project - Letter 3357 — Bateman, Robert to Darwin, C. R., (1862)". Retrieved 2009-02-09.
- "Darwin Correspondence Project - Letter 3356 — Bateman, James to Darwin, C.R., (1862)". Retrieved 2009-02-09.
- "Darwin Correspondence Project - Letter 3411 — Darwin, C. R. to Hooker, J. D., 25 Jan (1862)". Retrieved 2009-02-09.
- Darwin 1862, pp. 197–203
- Wallace, Alfred R. (1867). "Creation by Law". The Quarterly Journal of Science: 477. Retrieved 2016-05-20.
- Rothschild; Jordan (1903). "A revision of the Lepidopterous family Sphingidae.". Novitates Zoologicae, Volume IX. Supplement: 32.
- Beccaloni, George (2010). "Darwin and Wallace's Predictions Come True". Retrieved 2015-07-01.
- "AfroMoths". www.afromoths.net. Retrieved 2017-07-26.
- Darwin, Charles (1862). "On the various contrivances by which British and foreign orchids are fertilised by insects, and on the good effects of intercrossing". London: John Murray. Retrieved 2009-02-07.