Hawk moths and evolutionary predictions
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| A selection of Sphingidae moths that I photographed from the collection at London’s Natural History Museum. |
Commonly known as Hawk Moths, Sphinx Moths and Hornworms, these moths are important pollinators of orchids and other flowers.
Nectar tubes and hawk moth tongue lengths are often associated; Xanthopan morganii praedicta (centre) was famously predicted to exist by Charles Darwin and Alfred Russel Wallace based on the length of the nectar spur of the Madagascan Christmas star orchid (Angraecum sesquipedale). Note the length of the moth’s uncoiled proboscis in the photo above.
In a letter to Joseph Hooker in 1862, Darwin wrote:
“I have just received such a Box full […] with the astounding Angraecum sesquipedalia [sic] with a nectary a foot long. Good Heavens what insect can suck it.”
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| A hand-coloured lithograph of Angraecum sesquipedale by W.H. Fitch (1859) taken from Curtis’s Botanical Magazine. |
A few days later, Darwin wrote a second letter in which he postulated that this insect must be a moth, and in 1867 Wallace published an article in which he supported Darwin’s suggestion, remarking that the African hawkmoth 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!”
In 1903 (41 years after Darwin’s observation) this moth was discovered and named by Rothschild & Jordan after Wallace’s prediction that the moth would in fact be a hawkmoth. However, it was not before 1997 that it was finally confirmed that the Madagascan Christmas star orchid is actually pollinated by Xanthopan morganii praedicta.
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