It was the butterflies that informed them. Thomas Rupp, a doctoral student in ecology at the Paris-Lodron University in Salzburg, was walking in a mountain forest with his teammates near Athens, Greece, when he saw them: the insects which, in caterpillar form, feed on a particular species of plant called Aristolochia microstoma. “Everywhere I saw this butterfly fly,” says Rupp, “I knew there must be Aristoloche plants around.
Rupp crouched down to find the plant’s unusual flowers hidden among the rocks and leaves. They are dark merlot red and look like a swollen bulb connected to a narrow tube with a small pore called a stoma. It all looks a lot like the entrance to an intestinal tract. It’s not. It’s even stranger.
Environmentalists have long suspected that these flowers use a clever ploy to attract visitors, who will take their pollen with them to other flowers of the same species when they leave. Most flowers offer colorful petals or tons of sweet nectar in return for this service. But no A. microstomy. “They are liars,” says Stefan Dötterl, Rupp’s advisor and environmentalist. “They promise something. They seem to offer a reward, which they do do not to have. So they trick the pollinators into pollinating.
A tactic of “deceptive pollination” is not unheard of: some orchids have evolved to look and smell like insects that will try to mate with them, and the famous corpse flower attracts insects in search of rotting meat. But in a study published in May in the journal Frontiers in ecology and evolution, the team found that these plants attract pollinators by using a different death scent: the scent of dead beetles. This is the first report of a plant smelling like decaying invertebrates, and Rupp’s team shows how this unique evolutionary strategy works to trap unsuspecting flies.
It must be said that flies are weird too. phorids, the fly family which includes “coffin flies”, is known to lay eggs in the corpses of decaying beetles. The phorids also frequent human remains. They can be indicators of where a body is buried, and scientists can use them to estimate how long a person has been dead. “These are really important insects that people use for forensic entomology, and here they are visiting a flower that was supposed to mimic carcasses or leftovers,” explains Anne Gaskett, a behavioral environmentalist at the University of Auckland in New Zealand, who was not involved in the work. Gaskett studies how plants, mainly orchids, trick pollinators. “It’s a nice match between what you might predict and what they actually found. “