Certain flies specialise in feeding on bodily secretions from dead or dying bees. Picture a spider catching a bee in its web. As the bee struggles desperately to escape, a fly lands on it to feast on its juices, helping itself to the spider’s meal.

But that is not the most remarkable part. Or at least, not the only one.

One plant specialises in deceiving these flies. Its flowers give off the same scent as a bee that is dying or struggling to survive. Once inside, the flies are trapped for around 24 hours with absolutely nothing to eat, not even pollen or nectar. They are released only after they have had time to explore every part of the flower in search of food or an escape route, picking up a sticky “package” of the plant’s sperm along the way (yes, plants have sperm too, carried within their pollen).

Weak and hungry when they emerge, the flies may be “foolish” enough to head straight for the next deceptive flower, only to be trapped all over again. Along the way, they may deposit their sticky package, serving the plants’ dark and devious purpose: pollination, and ultimately more flowers to trap them in the future.

The botanical star of this extraordinary story is Ceropegia sandersonii, also known as the “parachute flower” for the parachute-like shape of its blooms.

This climber is native to South Africa, and it is far from alone in resorting to such tricks. Around 4–6% of plants, roughly 15,000 species, rely on deception for pollination. Some of the best-known examples are orchids whose flowers resemble female bees, luring in the males.

Physical mimicry is just one way flowers deceive insects. They can also use chemical signals to fool their pollinators. The delightful orchid Calypso bulbosa, found in the Rocky Mountains above Denver and Boulder, uses enticing scents from false anthers and the promise of nectar to attract bumblebees, yet offers no real nectar or pollen as a reward. Its scent varies so much from one flower to the next that the insects cannot associate a particular smell with being deceived. They fall for the same trick again and again.

Ceropegia stages a performance of its own, combining a complex blend of scents that mimic a dying bee with an ingenious trap.

Scientists knew that plants in the genus Ceropegia used deception to lure insects into their flowers, but exactly how they did it remained a mystery. They also knew that the flies usually responsible for pollinating them were kleptoparasites: food thieves that fed on fluids secreted by dead or dying insects, stealing a meal from other animals.

Only the females of these flies, often Desmometopa, are kleptoparasitic. Like female mosquitoes, which alone feed on blood, they need the protein in these secretions to produce eggs. Scientists had suggested that the flies followed airborne scent signals, known as alarm pheromones, released by trapped bees. Could Ceropegia be imitating those signals?

The researchers reasoned that, if Ceropegia flowers were mimicking the “food” of Desmometopa flies, their scent would contain an unusual blend of odours rarely found in flowers, matching those released by a dying bee.

Sure enough, kleptoparasitic Desmometopa flies were the flowers’ most frequent visitors. Most of the insects found inside flowers during the experiments were female, supporting the idea that the flowers mimic a scent the “ladies” simply cannot resist. And 60% of the scents released by Ceropegia flowers resembled those given off by European and South African honeybee subspecies when exposed to threats in experiments. The bees’ scent also varied considerably, and the flowers copied even that, producing highly variable scents of their own.

No other flower in the world releases the same combination of compounds as Ceropegia, and no insect does either, apart from this particular bee.