This clever plant mimics odor of injured ants to attract pollinators

By Stephen Beech

A plant is the first ever to be seen mimicking ants to attract pollinators.

The species of dogbane imitates the smell of injured insects to entice flies.

Researchers discovered that Vincetoxicum nakaianum - native to Japan - mimics the smell of ants attacked by spiders to attract the flies who, in the process of feeding, pollinate the flowers.

The discovery, published in the journal Current Biology, is the first case of a plant mimicking the odor of ants.

It reveals that the scope of floral mimicry is more diverse than previously imagined, according to the Japanese research team.

They explained that grass flies are attracted to the smell of their daily food: injured ants.

As they move from flower to flower in search of already injured prey, they also do the flowers a great service by pollinating them.

Because ants are one of the most widespread species, and ant mimicry has independently evolved in many invertebrate species, the research team said it stood to reason that plants could have also evolved to mimic ants in one way or another.

But such cases had never been reported, until now.

Dr. Ko Mochizuki, from the University of Tokyo, said: “I was working on another research project, and originally collected this species only as a 'reference' for comparison.

"By chance, I noticed chloropid flies gathering around its flowers in the nursery in the Koishikawa Botanical Gardens, and immediately realised that the flowers might be imitating dead insects.”

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He said his participation in an intensive training course in 2019 helped him recognise the fly species swarming the flower.

He was also familiar with some previous studies that described plants pollinated by chloropid flies emitting odors resembling those of insects.

Following his hunch, Dr Mochizuki set out to methodically observe the visitors on the flowers and compare the odors released by the flowers to odors released by various kinds of insects.

He found that the smell of ants being attacked by spiders was the closest match.

But there had not been any official publications of chloropid flies, or any other similar fly species, targeting ants hunted and injured by other animals, such as spiders.

Dr. Mochizuki turned to social media for more unconventional evidence.

He found online several amateur naturalists documenting what he had suspected: ants attacked by spiders, which then attracted "kleptoparasitic" organisms that steal food from other flies.

That gave him confidence to test the hypothesis behaviorally and confirm whether chloropid flies were really more attracted to the smell of ants attacked by spiders than to other smells.

Dr. Mochizuki said: “That moment, when I saw the flies on the flowers, was truly one of inspiration, a hypothesis suddenly taking shape.

"This experience taught me that unexpected discoveries often emerge from a combination of preparation and chance.”

Now he is preparing for his next project.

Dr. Mochizuki said: “I would like to investigate the evolutionary background of ant mimicry by comparing the pollination systems, evolutionary history, and genetic make-up of Vincetoxicum nakaianum and its close relatives."

He added: "In addition, since this study suggests that many forms of floral mimicry may remain hidden, I plan to explore other species, both within Vincetoxicum and in unrelated plant groups, to uncover further examples of potential mimicry.”