Parachute Plants Trick Flies with Honeybee Scent

The botanical kingdom has many interesting plants with unexpected powers of deception—often meant as a defense or a hunting tactic. Carrion flowers are a prime example, as they mimic the smell of rotting meat to attract scavenger beetles and flies to cover them in their pollen. Many carnivorous plants also attract insects with sweet odors and then devour them. Now, students from the Universities of Salzburg and Bayreuth have uncovered another scientifically astounding deceptive plant.

Described in Current Biology, a vegetable being dubbed a parachute plant uses chemical signals to trick carnivorous flies into thinking the insects they eat are wounded inside the plant—when really, it is a mere trick of the eye. When viewing parachute plants, it’s easy to notice they have cone shaped flowers decorated with needlelike hairs that point inward, giving the illusion that they themselves are carnivorous. They aren’t, but they are close to it.

Insects enter this plant’s flower and fall into a pit of pollen, and they are unable to escape from the needle like hairs meant to trap them in place. They cannot escape until the flowers wilt, and by that time, they are coated in the pollen, but why do these insects go inside? The plant does not have any conventional odors, sweet or smelly, that plants usually use to attract prey. The university students studying parachute plants asked two questions:  which insects are attracted to these plants? And what chemicals, if any, do the flowers make?

Collecting the trapped insects provided an easy answer to the first question. The plants attract flies from the Desmometopa group, a type of fly that sucks up the vital fluids that leak from honeybees when their bodies are pierced by spider fangs. Also, another study showed the flowers produced chemicals with four molecules—2-heptanone, geraniol, 2-nonanol, and (E)-2-octenyl acetate. These are the same four compounds found in bees when pierced by a spider fang or other type of object.

The researchers set traps with these chemicals, and, lo and behold, they attracted tons of these same flies. The four compounds are already well known to beekeepers. The 2-heptanone are produced when bees attempt to bite predators. The other compounds are used to notify the colonies of danger. Altogether, these compounds signal to the flies that a bee is in trouble, and they come investigate the release of the chemicals.

The fact of parachute plants developing the ability to mimic these four compounds speaks to the true versatility of these plants and evolution in general!

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