In the natural world, flowering plants attract pollinators through visual cues, such as showy petals, vibrant colors, organic shapes, or nectar guides. Other plants use fragrance instead—and it is not always pleasant.
The Aristolochia microstoma, found in Greece, attracts and traps pollinating coffin flies Megaselia scalaris when it emits a smell reminiscent of decomposing insects, reports Carly Cassella for Science Alert. Researchers suspect that it is the first known case of a plant that uses the scent of dead bugs to spread its pollen, rather than using the smell of carrion—or decaying vertebrates—like other plants do. The study was published this month in the open-access journal Frontiers in Ecology and Evolution.
While other flowers deceive pollinators with gorgeous blossoms, A. microstoma isn't as extravagant. The plant has small, brown, bulb-like flowers that look similar to the bowl of a tobacco pipe. The brown flowers easily blend into the forest floor near rocks and leaf litter and release the decay-like smell to entice pollinators to the flowers' opening, reports Isaac Schultz for Gizmodo.
Before, researchers thought A. microstoma was pollinated by ants and other insects crawling around in the leaf litter. However, when researchers observed 1,457 A. microstoma flowers, they found the petals trapped various flies belonging to the Megaselia genus, reports Science Alert. Coffin flies usually lay their eggs in decaying vertebrate corpses or feces, but the scent of decaying invertebrate corpses may also attract flies from the genus Megaselia, the researchers explain in a statement.
Plants belonging to the genus Aristolochia usually trap pollinators within their flowers through hairs that line the inside of the floral chamber. The hairs point towards the plant's sexual organs and prevent pollinators from leaving until the hairs retreat, Gizmodo reports. Stuck within the stinky flower, the flies end up depositing pollen they might have brushed up against inside, fertilizing the female parts of the plant, reports Science Alert. When the hairs recede, the fly emerges covered with pollen from the male parts of the plant and may spread it to another flower.
In A. microstoma, the plant uses its scent first to lure the flies into the trap. Researchers used laboratory techniques like gas chromatography and mass spectrometry to identify 16 chemical compounds that create the enticing aroma, per Gizmodo. They found oligosulfides, which smell like rotting meat. Bats often pollinate plants that produce oligosulfides. They also found a chemical compound known as alkylpyrazine 2,5-dimethylpyrazine, which gives off the scent of musty, roasted peanuts or cooked rice, Science Alert reports. In nature, alkylpyrazine 2,5-dimethylpyrazine is found in rodent urine and in the carcasses of decaying beetles.
The researchers concluded not many flowering plants give off the scent that A. microstoma does, suggesting the plant releases the smell to attract the coffin flies specifically, Gizmodo reports. Otherwise, the plant would also attract other insects that crawl along the forest floor. The researchers plan on testing how attractive the scent compounds are to coffin flies to confirm if A. microstoma is the flies' only source for pollination, Science Alert reports.
"We conclude that A. microstoma likely uses a strategy that has never been reported before: its flowers mimic the smell of invertebrate carrion to attract and imprison pollinators," says co-author and botanist Stefan Wanke from the Dresden University of Technology in Germany, in a statement. "The peculiar orientation of the flowers close to the ground may also help, as pollinating coffin flies search for breeding sites or food close to the ground, in leaf litter or between rocks."