Strategy of Japanese endemic plant "tachigashiwa" discovered by the University of Tokyo — Mimic the scent of ants

Research Associate Ko Mochizuki of the Graduate School of Science at the University of Tokyo, revealed that the flowers of tachigashiwa (Vincetoxicum nakaianum (Apocynaceae)), a plant endemic to Japan, are "ant-mimicking flowers" that attract insects of the family Chloropidae as pollinators by mimicking the scent of ants attacked by spiders. While ant mimicry by arthropods has evolved independently more than 70 times, this is the world's first discovery of ant mimicry in flowers. The findings were published in Current Biology.

Angiosperms have evolved flowers with diverse colors and scents through their interactions with animals that carry pollen, such as insects and birds (pollinators). Among these, deceptive flowers that attract pollinators by mimicking nectar-bearing flowers, decaying fruits or flesh, or specific female insects are particularly fascinating phenomena observed in nature. Examples include: Cypripedium marcanthum var. rebunense, which is thought to mimic the nectar-bearing Pedicularis chamissonis var. rebunensis; Stapelia and Amorphophallus titanum, which attract flies and beetles with carrion-like odors; some species of Epipactis that emit aphid pheromones; and Dracula species that mimic mushrooms-all demonstrating this diversity.

Although deceptive flowers are known in many taxonomic groups, recent years have seen little research actually "searching for new deceptive flowers." Therefore, fundamental questions remain insufficiently answered, such as how widely deceptive flowers are distributed across taxonomic groups and what models they mimic.

Mochizuki gained inspiration after observing numerous insects of the family Chloropidae swarming the flowers of tachigashiwa (Apocynaceae, genus Vincetoxicum) cultivated at the Koishikawa Botanical Garden in Bunkyo City, Tokyo Prefecture. The family Chloropidae includes kleptoparasitic species known to scavenge on prey body fluids by taking advantage of hunts by predators such as spiders and mantises. Previously, the pollinators of tachigashiwa were unknown, but this observation led to the hypothesis that "tachigashiwa might be a deceptive flower that mimics the scent of fresh insect carcasses," prompting the research.

First, pollinator surveys totaling 150 hours were conducted from 2021 to 2025 at the Nikko Botanical Garden, the native habitat of tachigashiwa, and its surroundings. The surveys revealed that four species of Chloropidae insects, including Dasiops latifrons, serve as pollinators.

Next, analysis of the floral scent using gas chromatography-mass spectrometry detected a total of 26 volatile compounds. Among these, five components-nonane, undecane, octyl acetate, decyl acetate, and methyl 6-methylsalicylate (6-MMS)-were consistently detected. In field experiments using a synthetic mixture that reproduced the floral scent ratio of these five components, Chloropidae flies of the same species as the pollinators were attracted to the mixture. Moreover, comparison using subtraction mixtures with components removed one at a time revealed that the attractiveness decreased significantly when decyl acetate and 6-MMS were absent. It was also found that these two components had no effect individually and only exhibited attractiveness when combined.

Furthermore, to explore which insect's scent this resembles, the research team consulted Pherobase, a database of infochemicals, and investigated insects possessing the five major components of the floral scent. The results showed that taxonomic groups such as Hymenoptera, Coleoptera, and Hemiptera shared some of these components, with particularly frequent confirmation that the subfamily Formicinae of the family Formicidae possessed both decyl acetate and 6-MMS.

Therefore, a total of 38 species of ants, ground beetles, and true bugs were collected around the native habitat of tachigashiwa, and the scents released upon stimulation were analyzed. The results revealed that the scent released by Formica japonica and its closely related species Formica hayashi when preyed upon by spiders closely resembled the floral scent of tachigashiwa. Behavioral experiments also confirmed that F. japonica preyed upon by spiders attracted Chloropidae flies.

From these results, the research team concluded that tachigashiwa attracts Chloropidae flies, its pollinators, by mimicking the "scent of Formica ants preyed upon by spiders." While pollination by kleptoparasitic flies has been known in Aristolochia species that emit the scent of certain assassin bugs and Ceropegia species in the Apocynaceae that mimic honeybee alarm pheromones, this represents a novel mimicry model distinct from these examples.

In the future, the research team aims to further clarify the life history of Chloropidae and their interactions with ants. Also, they will advance analysis of pollination modes and phylogenetic relationships among related species in the genus Vincetoxicum to elucidate the evolutionary process of the unique trait of ant-mimicking flowers, as well as to continue discovering new deceptive flowers among related species.

Journal Information
Publication: Current Biology
Title: Olfactory floral mimicry of injured ants mediates the attraction of kleptoparasitic fly pollinators
DOI: 10.1016/j.cub.2025.08.060