Blister beetles are herbivorous insects that gnaw on mugwort or cabbage, but some species are carnivorous and eat honey bee eggs. How can a beetle without wings get into a hive? Even an ironclad defense was useless against a "femme fatale." Honey bees were fooled by the floral scent emitted by the blister beetle and were drawn to its guise as a mate.
A team led by Tobias G. Köllner at the Max Planck Institute for Chemical Ecology said on Jan. 15 that larvae of the European blister beetle Meloe proscarabaeus emit floral scents to lure honey bees. The researchers noted this is the first confirmed case of an animal mimicking a flower's scent. The findings were first posted on the preprint server bioRxiv before journal publication.
◇ At the tip of the stem, it emits floral scents to lure honey bees
The blister beetle is called "blister beetle" in English. Its wings are degenerate, so when it encounters predators, it does not fly away but secretes cantharidin, which causes blisters. In medieval Europe, this substance was also used as an aphrodisiac. The studied species, Meloe proscarabaeus, belongs to the blister beetle family and, as its name suggests, has a navy body.
Blister beetle larvae gather at the tips of twigs or leaves and cling to approaching honey bees. The target is not the adults. They hitch a ride on a bee's back to enter the hive and eat the eggs. They even consume the honey and pollen that bees have stored for their offspring. Once fully grown, they leave the hive and live on leaves.
To find out why honey bees approach blister beetle larvae, the researchers first collected adults and reared them in the lab. After mating, the beetles laid eggs underground. Three weeks later, the hatched larvae, about 3 centimeters long, scrambled up to the tips of plant stems. Noting that in nature bees are drawn to larvae clustered at stem tips, the team hypothesized that the larvae release some attractant.
Gas chromatography of volatiles from the larvae detected monoterpenoids, light molecules that are rare in insects but common in plants. Among them, the abundant linalool oxide and lilac aldehydes are compounds flowers release to attract bees and butterflies. Köllner said, "When I saw the unexpected analysis results, I thought, 'This isn't an insect, it's a flower.'"
The team then tested whether bees actually seek out larvae drawn by floral scents. In a Y-tube maze, they placed Meloe proscarabaeus larvae at one end and wheatgrass at the other, and introduced red mason bees (Osmia bicornis), a solitary species, at the entrance. Both males and females chose the larvae over the wheatgrass. Bees always seek flowers over wheatgrass. The bees had mistaken the blister beetle larvae for flowers.
The researchers also identified the biosynthetic pathway that larvae use to make floral scent components. Mimicking this, they synthesized monoterpenoids extracted from the larvae. The artificial scent attracted not only red mason bees but also the ground-nesting plasterer bee (Colletes similis), the buff-tailed bumblebee (Bombus terrestris), and even the western honey bee used in beekeeping (Apis mellifera), the team said.
◇ It also mimics the appearance of female bees to lure males
Blister beetles are already known as experts at deceiving bees. In 2000, a team led by John Hafernik at San Francisco State University released in the journal Nature that larvae of Meloe franciscanus in the Mojave Desert infiltrate hives by disguising themselves as female bees.
Desert-dwelling Meloe franciscanus lay eggs underground, and usually thousands of larvae hatch at once. The larvae soon crawl up the tips of nearby twigs or leaves. They cluster into a ball, and solitary male bees in the desert mistake this for a female and rush in to mate. At that moment, the larvae climb onto the male's back.
The problem is that after mating, male bees do not return to the hive. Only the queen and worker bees can enter the hive. Larvae that hitched a ride on a male must transfer to a female. The larvae seize the moment when the male mates with a real female and move onto the female. Ultimately, the larvae ride the female to enter the hive with ease.
Scientists at the Max Planck Institute explained that European Meloe proscarabaeus can call female worker bees directly with floral scents and reach the hive without needing a transfer. They added that European Meloe proscarabaeus larvae are orange, creating a visual effect that also makes them look like flowers.
◇ It even mimics honey bees' mating signal chemicals
Plants deceive bees, too. Orchids evolved flowers shaped like female bees to lure males without offering a drop of nectar. The orchid's "femme fatale" strategy does not stop there. Orchids also mimic the pheromones secreted by female bees to entice males. Pheromones are substances insects release outside the body to find mates or send warning signals to peers.
Blister beetle larvae also have chemical weapons like orchids. In a 2006 paper in the Proceedings of the National Academy of Sciences (PNAS), Leslie Saul-Gershenz of the San Francisco Institute for Conservation Research released that American Meloe larvae mimic not only the shape but also the pheromones of female bees to deceive male bees.
Experiments showed that even if a structure identical to the larvae clustered at a stem tip was present, it failed to attract male bees unless coated with secretions from the larvae or female bees. The team explained that the larvae cluster by the thousands to mimic a female bee's form while simultaneously boosting pheromone concentration. Is there any bee that would not fall for the blister beetle larvae's multi-layered con?
References
bioRxiv (2026), DOI: https://doi.org/10.64898/2026.01.15.699641
PNAS (2006), DOI: https://doi.org/10.1073/pnas.0603901103
Nature (2000), DOI: https://doi.org/10.1038/35011129