FOREST OF LOBAYE, Central African Republic (AFP) — Suspended from branches high above the ground, Nicolas Moulin looked through his binoculars over a seemingly endless sea of emerald green.
Somewhere beneath the forest canopy was the African giant swallowtail: the largest butterfly to appear by day on the African continent, virtually unrecorded in scientific annals but known to be venomous.
The species, known in Latin as Papilio antimachus, was discovered in 1782.
Its black-streaked orange-brown wings are extraordinary. They reach up to 9.8 inches across, making it one of the largest butterflies in the world.
But, just as remarkable, nobody has ever been able to study the creature in its state as caterpillar or chrysalis — keys to understanding its life cycle and longevity.
Seeking to unlock the mystery, a privately-financed French expedition of about 20 people set up camp in the far south of the Central African Republic, on the banks of the Lobaye river, which winds like a copper snake through primary forest.
"This is a place for poachers — the male (butterflies) come to ingest mineral salts on the bank and are captured," Moulin said from his perch 130 feet above the ground.
Collages created from the wings of butterflies are a prized art form in the CAR and provide a living for many hunters. Abroad, a giant swallowtail specimen can sell for $1,700.
The males flutter close to the ground but the females live right up in the forest canopy. There, they feast on flowers exposed to direct sunlight and are hardly ever seen.
"This species, like many others, is becoming increasingly rare," said the expedition's senior scientist, entomologist Philippe Annoyer.
But how rare is the big question.
P. antimachus is so elusive that there is insufficient data to determine its conservation status.
"The details we have date from the 1960s and consist of half a page in a scientific journal," said Annoyer.
The researchers speculate that the giant butterfly most likely gets its venom when its caterpillar ingests the leaves of Strophanthus gratus — a thick, woody liana that winds among the treetops and bears flagrant flowers.
The team planned to pinpoint the flowers in the forest canopy with the help of a drone.
Then, it was hoped, they could set up a sophisticated network of ropes enabling people to move around the heights to explore the whole length of the liana.
That way, they might find a P. antimachus caterpillar, according to this scheme... even though nobody knew quite what these caterpillars looked like.