On this date, in a letter to J.D. Hooker, Charles Darwin made a prediction that was not confirmed until very recently. Darwin had recently received many orchids from James Bateman, including one very intriguing species called the star-of-Bethlehem or comet orchid (Angraecum sesquipedale Thouars). Native to Madagascar, the comet orchid blooms beginning in December and is phalenophilic, meaning “moth-loving”. Its waxy white flowers are scentless during the day and both highly visible and fragrant after dark to attract the night-fliers. Most notably, each flower has a remarkable spur or nectary up to 30 centimeters (12 inches) long, but only the tip of the spur contains nectar. In today’s letter, musing on what could suck the nectar from such a flower, Darwin predicted that an insect with an extremely long proboscis would be discovered and that it would be the major pollinator of the orchid.
In 1856, a sphinx moth had been discovered in southeastern Africa. It was named Macrosila morgani, Morgan’s sphinx moth. But no one associated the moth on the continent of Africa with the orchid on Madagascar. Charles Darwin died in 1882. Twenty-one years after his death, a subspecies of Morgan’s sphinx moth was discovered on the island. And it fit Darwin’s prediction, having a proboscis long enough to reach into the tip of the orchid’s nectary. In 1903, the sphinx moth’s genus was reclassified to Xanthopan and the ‘predicted’ Madagascan moth was named Xanthopan morgani subspecies praedicta (although the subspecies was later determined to be invalid, since it is identical to the mainland form of the species).