Wallace's sphinx moth.

Darwin and fellow naturalist Alfred Russel Wallace predicted the existence of Wallace's sphinx moth from an orchid with an extremely long nectar tube.

Name: Wallace's sphinx moth (Xanthopan praedicta)

Where it's found: Lowlands of Madagascar

What it eats: Nectar of Darwin's orchid (Angraecum sesquipedale)

Why it's awesome: In 1862, Charles Darwin received a Madagascan orchid in the mail. The flower had an extraordinarily long nectar tube, called a nectary, measuring 1 foot (30 centimeters) in length. In a letter to a friend, he described the orchid as "astounding" and wondered what pollinator might be able to feed on the nectar. "Good Heavens what insect can suck it," he wrote. A couple of days later, in another letter to the same friend, he gave a more specific prediction: "what a proboscis the moth that sucks it must have!"

Madagascan sphinx moth, Xanthopan morganii praedicta.

While Darwin predicted that the orchid would be pollinated by a long-tongued moth, when naturalist Alfred Russel Wallace described the orchid in 1867, he said some of the larger species from the the Sphingidae family of moths (known as sphinx moths or hawk moths) had proboscises almost as long as the nectary of Angraecum sesquipedale.

The two naturalists were proved right when such a long-tongued moth was found in Madagascar. It was described in 1903 as a subspecies of the Morgan's sphinx moth (Xanthopan morganii) and given the scientific name X. m. praedicta. It wasn't until the 1990s that the pollination predicted by Darwin and Wallace was observed and photographed.

Darwin's orchid Angraecum sesquipedale.

More recently, the moth was determined to have the longest insect tongue. And a taxonomic study published in 2021 concluded that the insect should be classified as its own species and was named Xanthopan praedicta.

"Imagine my excitement in 2019 when I unrolled the proboscis of a Wallace's sphinx moth that had arrived on the balcony of a research station in Madagascar!" David Lees, curator of moths at the Natural History Museum in London and co-author of the 2021 study, told Live Science in an email. "Its 28.5-cm-long [11.2 inches] proboscis turned out to be the longest yet recorded for any insect, let alone hawk moth."