Moth Tongues and Orchids-Darwin’s Prediction Came True

On my lecture circuit on pollinators, I always like to include the fascinating story of Charles Darwin and his prediction of the existence of a hawk moth pollinator of the Comet Orchid in Madagascar.

Color plate from Ernst Haeckel's Kunstformen der Natur, 1904
Color plate from Ernst Haeckel’s Kunstformen der Natur, 1904

Orchids are known for their extreme measures of restricting access to nectar to get the right pollinator to visit and it was the Comet Orchid that led to the creation of a famous hypothesis by the renowned biologist.

"Angraecum sesquipedale - Diogo Correia" by Diogo Correia
The long thread like pieces are the spurs of the flower that contain nectar – Diogo Correia

The story starts in 1862, when naturalist Charles Darwin received some live Comet Orchids from the famous orchid collector John Bateman. Grown as highly prized orchids at Kew Gardens and by Victorian plant collectors,  these beautiful arrivals from Madagascar of the Star or Comet Orchid(Angraecum sesquipedale) were highly coveted.

From Wikipedia
From Wikipedia

 Darwin after examining the large white waxy flower which had a very long spur of over 12 inches with a few drops of nectar in its lower tip, predicted the existence of an insect, likely a hawk moth, with a great proboscis (tongue), that could reach into the spur to lap up the nectar.  The problem was that there was no known insect that had ever been observed in Madagascar or anywhere for that matter, that had such a long tongue.

Some moths have very long tongues
Some moths have very long tongues

Many people, including fellow scientists, believed the idea of a insect having a foot long tongue to be ridiculous, but Darwin held firmly to his belief. Darwin was predicting the existence of an otherwise unknown species of insect based purely on the size of the flower and his understanding of the mutual evolution of orchids and insects. His theory of natural selection would be reinforced showing how different organisms respond to each other’s evolution according to form and function if such an insect was discovered.

"NHM Xanthopan morgani" by Esculapio - Own work
“NHM Xanthopan morgani” by Esculapio – Own work

After Darwin’s death and more than twenty years later after his original prediction, a large hawk moth (Xanthopan morganii praedicta) was indeed discovered in Madagascar. Notice the latin  “praedicta” in the name. But only recently in the 1980’s were pictures available of the actual moth sucking nectar from the orchid. And now we have videos of this extraordinary event happening. The first one explains Darwin’s prediction and the second is of the extraordinary pollination event.

 

 

 

Many flowers and especially Orchids have evolved over millions of years mutual evolutionary strategies for pollination. The insect benefits by obtaining pollen and nectar that it needs to survive and the orchid ensures the survival of the species.

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