To measure the butterfly's proboscis, scientists immerse preserved specimens in a water bath overnight to soften its tongue. So researchers can measure its length. The Wallace's sphinx's proboscis measures between 15 and 28.5 centimeters long.
Wallace's sphinx, the butterfly with an astonishing physical peculiarity
Certain species stand out for their astonishing physical particularity. The giant squid, for example, with its eyes measuring 27 cm in diameter, wins the prize for the animal with the most imposing eyeball. As for the African hippopotamus, it has the largest jaw of all land animals, since it can open it 180°.
photo credit: MNHN language of Wallace's Sphinx
For the largest language in the world, it is indeed an insect that stands out, proportionally to its size, from other species. This is Wallace's sphinx. when fully unfurled, its trunk reaches 28.5 centimeters. In nature, such a long tongue is useful for pollinating plants… a little less useful for flying when it is deployed.
In addition, it makes it vulnerable to predation by bats and other birds when they are feeding. Lemurs can also easily catch them when they move towards orchids. To compensate for this natural handicap, the butterfly unfurls its trunk only when it approaches the flower. Once his feast is complete, he rolls it up again.
The history of the discovery of the species
The discovery of this species begins with the discovery of a flower, a Malagasy orchid ( Angraecum sesquipedale), by Charles Darwin in 1862. The latter is provided with a nectar tube 30 centimeters long. The British naturalist wonders how this species can be pollinated, and says that the insect capable of this action is necessarily provided with an extremely long proboscis, to be able to recover the nectar from the plant.
In 1867, it was the turn of Alfred Russel Wallace, also a British naturalist, to reflect on the question. According to him, a species of sphinx is probably the author of this feat. “It can be predicted with certainty that such a butterfly exists in Madagascar, and naturalists who visit that island should search for it with as much confidence as astronomers have searched for the planet Neptune, and they will be as successful”.
Around 1903, this species of hawkmoth was thought to be a subspecies of the Morgan hawkmoth ( Xanthopan morganii ). It was only in 2021 that a new study affirmed that this sphinx is indeed a species in its own right, named Xanthopan praedicta. Indeed, measurements of the species' trunks are carried out in museums and private collections. Xanthopan praedicta has a proboscis on average 6.6 cm larger than the Xanthopan morganii.
A proposed taxonomic change
This taxonomic change is proposed in the journal Antenor which publishes the study by a team led by Professor Joël Minet. Dr David Lees, curator of moths at the Natural History Museum, speaks of his enthusiasm in the press release. “The taxonomic change we are proposing today finally gives long-deserved recognition, at the species level, to one of Madagascar's most famous endemic species.”
The Wallace's Sphinx is found only in Madagascar. According to the museum press release, its tongue evolved by elongating “to the rhythm of the long nectar tube of the orchid”. Ultimately, this species of orchid became entirely dependent on the pollination of this butterfly, although the reciprocity is not true: the butterfly is capable of pollinating other plants.
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