How Deceptive Can an Orchid Be?

Aug. 12, 2009 — -- Charles Darwin would have loved it.

Scientists have found that an orchid on the Chinese island of Hainan is even trickier than most orchids, admired by the great naturalist for their cleaver abilities to deceive pollinators.

Unlike many other orchids, the Dendrobium sinense doesn't produce an aroma that will lure bees into its boudoir, probably because bees don't serve as its pollinators.

The white orchid depends on the hornet Vespa bicolor to spread its pollen, but it has developed a self-serving technique to get the hornet to do it. The orchid releases a chemical that produces an aroma that is identical to the smell made by bees that are under attack.

The hornet normally captures bees to feed to its larvae, so when it smells the alarm pheromone it figures bees are inside the orchid, and they are in distress and thus would be easy victims. So the hornet plunges into the orchid like a cruise missile.

But there are no bees there. Only pollen, which clings to the body of the hornet. The hornet moves on, getting nothing for its efforts, and it spreads the pollen to other orchids in the Bawangling National Nature Reserve in Hainan.

More Than 20,000 to 30,000 Species of Orchid Exists

Scientists in China and at the University of Ulm in Germany spent 121 hours studying the orchid, watching hornets as they "pounced on the red center of the flower, much like their behavior when attacking prey," according to their study, published in Current Biology.

That may be among the most insidious routines in the enormous family of orchids, which numbers between 20,000 and 30,000 species and is the largest and most diverse plant family on Earth. Orchids flourish all over the planet, from north of the Arctic Circle to an island off Antarctica, which is why they fascinated Darwin.

Darwin turned to orchids for evidence to support his theory of natural selection. How had they adapted to virtually every climate on the Earth?

Orchids come in nearly all sizes, in all shapes and in all colors except black. Most of them cling to trees, escaping from a jungle floor that has so many aggressive plants that they would likely have been crowded out. So they live on air instead of soil, thriving under conditions that would be impossible for nearly all other plants.

Orchids Date Back at Least 76 Million Years

Three years after publishing "On the Origin of Species" in 1859, Darwin published his book, "On the various contrivances by which British and foreign orchids are fertilized by insects," documenting how different orchids had evolved different methods to get insects - especially bees - to work as their pollinators. Thus they were very efficient at widening their gene pool and ensuring healthy stock.

That partly explains why they have survived for so long. Biologists at Harvard University found a fossilized orchid a few years ago that suggests orchids were around during the age of the dinosaurs. The fossil, preserved in amber, dates orchids back to at least 76 million years ago, and this rare specimen didn't die alone. The amber also had a bee with pollen on its back.

So bees have flourished, along with the orchids they unwittingly serve, and they have adapted to changing conditions quite well, a fact that would please Darwin immensely. Brendan Borrell of the University of California, Berkeley, spent three years collecting bees all over Costa Rica and Panama and found that orchid bees are exceptionally well equipped to suck up the thick nectar from inside an orchid.

Some have very long tongues, which gives them access that would be denied to other bees with shorter tongues.

It takes awhile, like sucking up juice with a straw from a water melon. But it's worth the time, Borrell reported. This bee dines on nectar that is up to 10 times the quantity of nectar from other flowers serviced by bees.

So not only do orchids support Darwin's conclusions. So do the bees. Variety is not just the spice of life, it is also the key to survival. And it is the reason orchids are considered by many scientists to be the most highly evolved flowering plants on Earth.

In her delightful book, "The Orchid Thief," Susan Orlean describes some of the more bizarre orchids.

"One species looks like a German shepherd dog with its tongue sticking out," Orlean writes. "One species looks like an onion. One looks like an octopus. One looks like a human nose. One looks like the kind of fancy shoes that a king might wear. One looks like Mickey Mouse. One looks like a monkey," and so on.

Though They Appear Fragile, Orchids Are Quite Resilient

And they don't all smell like the purple beauty a lad might pin on his prom date. One, according to Orlean, smells like rotting meat, and insects like that. Others smell like chocolate, or other flowers that insects like to visit.

Although many appear fragile, they are surprisingly resilient, and some experts think an orchid plant could live forever, given the right circumstances. But alas, like so many other plants and animals, the orchid's world is shrinking and growing less hospitable.

Borneo's rain forests are home to at least 2,500 orchid species, but they are threatened by forest fires, illegal logging, and poachers, and that includes some very wealthy orchid lovers around the world who will stop at nothing to add to their collections. One recent study indicates that the forests, and the orchids within them, could vanish within a few years.

And in Africa, according to the Wildlife Conservation Society, orchids in the highlands of Tanzania are being "virtually strip-mined" because they are prized for a sort of vegetarian sausage.

Although orchids are protected from poaching by international conventions, business is booming. Orlean estimates that international trade in orchids brings in $10 billion a year.

Some species undoubtedly will be lost in the years ahead. But as Darwin suggested so long ago, these are very clever plants. They will probably be around long after we are gone.