In 1862, the gardener James Bateman sent several specimens of the Christmas
orchid to Charles Darwin. This orchid was first planted in Britain in 1855 and it did
not blossom until 1857. It had been discovered several decades before by the
French botanist Louis-Marie Aubert du Petit-Thouars in Madagascar in 1822. The
most significant aspect of this flower is the length of its spur. It measures 20–35 cm
from the tip to the lip of the flower.
In 1862, Charles Darwin published his book titled “Fertilization of Orchids”,
where he predicted that there should be a moth with a proboscis of a similar size.
Darwin knew that the Christmas orchid should be pollinated by a moth with a
proboscis that could get to the bottom of the flower given that the nectar is stored
in the lower 5 cm of its tubular spur. There should be a moth with a proboscis of a
similar length, able to reach the nectar from the outside of the flower.
At that time, the reaction in the scientific community was not welcoming.
Darwin had to endure some teasing. No one had ever discovered a moth with a
two-handspan proboscis.
The moth that pollinates the Christmas orchid was discovered later on in
Madagascar in 1903 and it had, indeed, a 25–30 cm long proboscis. It was baptised
with the name of “Xanthopan morganii praedicta”. The qualifier “praedicta” refers
to the prediction made by Darwin. We had to wait for the arrival of the 21st century
for it to be filmed in action for the first time.
How could Darwin be sure of the existence of that moth? Would it not be possible
that another type of insect was responsible for this orchid’s pollination? For
Darwin, the reasoning was simple. Tubular flowers of pale or white colours that
open at night belong to the floral syndrome called sphinxophilia. Such flowers are
usually pollinated by sphinginae (sphinx moths). These moths have a very long
proboscis and obtain nectar while in flight over the flower, similar to what hummingbirds
do. That is, sphinxophilias are pollinated by sphinginae. If a sphinxophilia
has a 35 cm long spur and the nectar is located in its lower 5 cm, there must
be a sphinginae with a 30 cm long proboscis. Simple. Forty-one years passed by
until that sphinx moth was discovered and 140 years until it was filmed.