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New Moth Species Found In Madagascar Has The Longest Tongue Of Any Insect

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The insect, known as "xanthopan praedicta" or "Wallace's sphinx moth," possesses a nearly one-foot-long tongue.

Charles Darwin got an intriguing notion when studying the long-necked Madagascar star orchid in 1862. He reasoned that some insects must have tongues long enough to eat on the plant. "What bug can suck it!" he shouted to a buddy.

Though such a moth was later recognised as Wallace's sphinx moth or Xanthopan morgani praedicta in 1903, it was classified as a subspecies of the Morgan's sphinx moth, a hawkmoth found in Africa. The two moths are now thought to be distinct species, according to experts.

Their tongue lengths are the most noticeable of their variations. The tongue of Morgan's sphinx moth is around three inches long, but the tongue of Wallace's sphinx moth is about one foot long. The moth, now known as xanthopan praedicta, possesses the longest tongue of any known insect.

"Imagine my delight as I unrolled and measured the proboscis [tongue] of a male Xanthopan in the Madagascan rainforest, realizing it was probably the global record holder," exclaimed Dr. David Lees, a moth curator at the National History Museum in London and one of the authors on a recent paper about the moth.

"The taxonomic modification we now propose finally provides long-deserved species status to one of the most famous of all Malagasy endemics," he said.

Lees studied the distinctions between Morgan's sphinx moth and Wallace's sphinx moth with Jol Minet, an entomologist at the Institute de Systématique, Évolution, Biodiversité in Paris. The latter was named after British naturalist Alfred Wallace Russel, who, like Darwin, hypothesized that a moth developed to eat Madagascar star orchids.

"That such a moth exists in Madagascar may be confidently anticipated, and naturalists who visit that island should seek for it with as much confidence as astronomers sought for the planet Neptune, and they will be as successful," Russel said.

Though the later called Xanthopan morgani praedicta (or predicted moth) was previously considered to be a subspecies of Morgan's sphinx moth, Lees and Minet discovered that they are in fact distinct species. For starters, the two moths vary genetically by 7.6 percent.

"This is much more than you'd expect between different species," Lees said.

Lees and Minet also discovered 25 physical differences, including the tongues of the moths. Researchers soaked moth specimens from around the world in water overnight to determine their length. The tongues were then carefully unrolled (and measured). Wallace's sphinx moth tongues were 6.6 centimetres longer on average than Morgan's sphinx moth tongues.

Because the tongues were too long to show, researchers rolled them back into the moths' heads.

Lees and Minet also discovered differences between Morgan's sphinx moth and Wallace's sphinx moth. The male/female genitalia, wing shapes, and colour patterns of the two moths differ.

"The underside of the Madagascar hawkmoth is pinkish, whereas the underside of the African hawkmoth is whitish or yellowish," Lees explained.

Despite the fact that there are hundreds of species of similar hawkmoths in the tropics, Wallace's sphinx moth can only be found in Madagascar. It has developed a close relationship with the Madagascar star orchid there.

However, the moth's long tongue can be dangerous. It cannot fly with its tongue extended — the moth only extends its tongue after landing on an orchid — and it is prey to predators such as bats.

Nonetheless, Wallace's sphinx moth appears to have thrived in Madagascar, where researchers discovered that moths across the island share the same DNA.

"The fact that I discovered one of these moths in a remote forest in southwest Madagascar suggests that it can fly hundreds of kilometres," Lees explained.

In this way, Wallace's sphinx moth embodies many of Darwin's evolutionary theories. Its long tongue allowed it to survive — and thrive — in the jungle after it evolved to feed on the Madagascar star orchid.