Plants That Mimic the Scent of Ants

To sustain the cycle of life, plants have evolved an extraordinary diversity of flowers and fragrances that attract pollinators. Among the strategies used in this evolutionary process, mimicry stands out as particularly ingenious. By imitating the appearance, scent, or other characteristics of organisms, plants can deceive specific insects into visiting their flowers. A recent study revealed that the plant Vincetoxicum nakaianum attracts flies for pollination in a remarkable way, uncovering a previously unknown form of floral mimicry.

Vincetoxicum nakaianum（圖片來源：Qwert1234，採用 CC BY-SA 3.0 授權）

Japanese biologist Ko Mochizuki observed that large numbers of chloropid flies (family Chloropidae) gather around flowering individuals of V. nakaianum in the Koishikawa Botanical Garden at the University of Tokyo. Many species in this fly family are kleptoparasites: they feed on the body fluids of insects that have been injured or captured by other predators. The presence of these flies around the plant therefore suggested that their attraction might somehow be linked to this feeding habit.

Through more than 150 hours of field observation and sampling, researchers recorded four chloropid fly species visiting V. nakaianum: Conioscinella divitis, Polyodaspis ruficornis, Tricimba lineella, and Tricimba japonica. These flies serve as the plant's primary pollinators. They land on the flowers to drink liquid secretions and sometimes even mate there. Their behavior closely resembles the way kleptoparasitic flies gather around insects that have been attacked by predators, suggesting that the plant might be imitating such prey-related cues.

Vincetoxicum nakaianum flowers attracting chloropid flies（感謝 Ko Mochizuki 提供）

Chemical analysis of the floral scent revealed five volatile compounds: nonane, undecane, octyl acetate, decyl acetate, and methyl-6-methyl salicylate. Experiments showed that the last two compounds play the key role in attracting the flies. Interestingly, neither compound is attractive when presented alone; they must act together to form an effective signal. Decyl acetate and methyl-6-methyl salicylate are chemicals typically found in ants, especially species belonging to the subfamily Formicinae.

When researchers examined two common Japanese ants, Formica japonica and Formica hayashi, they found that ants attacked by spiders released volatile chemicals strikingly similar to the floral scent of V. nakaianum. Both included decyl acetate and methyl-6-methyl salicylate. However, crushed ants did not attract the flies, indicating that these volatiles originate from physiological responses triggered during predator attacks rather than from simple tissue damage.

The scent produced by V. nakaianum flowers therefore represents a form of olfactory mimicry: the plant imitates the odor emitted by injured ants. This discovery provides the first clear evidence that a plant can use ants as a model for floral mimicry, specifically copying the “distress scent” ants release when attacked. For kleptoparasitic flies, such a smell signals a potential feeding opportunity. When the flies arrive expecting prey, they instead encounter flowers, and while feeding on floral secretions they inadvertently transfer pollen.

In this way, V. nakaianum does not reward insects with abundant nectar like many other flowering plants. Instead, it exploits the flies' instinctive response to the scent of wounded prey, effectively deceiving them into acting as pollinators.

The discovery also carries broader implications for chemical ecology. Methyl-6-methyl salicylate has rarely been detected in plants. In ants, this compound can function as a trail pheromone, a mating signal, or an alarm substance. The ability of V. nakaianum to synthesize and release this molecule suggests that the plant has evolved metabolic pathways capable of producing chemicals normally used in animal communication, adapting them for its own reproductive strategy.

By mimicking the distress signal of injured ants and luring flies searching for food, V. nakaianum turns unsuspecting scavengers into carriers of pollen. This interaction highlights the intricate complexity of plant–insect relationships—an evolutionary strategy so subtle that its sophistication remains hidden until carefully investigated.

Author: Shui-Ye You

Reference:

Mochizuki Ko. (2025). Olfactory floral mimicry of injured ants mediates the attraction of kleptoparasitic fly pollinators. Current Biology.