It was the butterflies that tipped them off. Thomas Rupp, a PhD student in ecology at the Paris-Lodron University of Salzburg, was walking through a mountain forest with his teammates near Athens, Greece, when he saw them: the insects that, when in caterpillar form, feed on a special kind of plant called Aristolochia microstoma. “Wherever I saw this butterfly flying,” Rupp says, “I knew that there must be some Aristolochia plants around.”
Rupp crouched down to find the plant’s unusual flowers lying hidden among rocks and leaves. They are a dark merlot red, and they look like an inflated bulb connected to a narrow tube tipped by a small pore called a stoma. The whole thing looks a lot like the entry to an intestinal tract. It’s not. It’s even weirder.
Ecologists have long suspected that these flowers use a clever ploy to attract visitors, which will carry 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 exchange for this service. But not A. microstoma. “They are liars,” says Stefan Dötterl, Rupp’s adviser and an ecologist. “They promise something. They seem to offer a reward which they do not have. So they trick the pollinators into pollination.”
A “deceptive pollination” tactic isn’t unheard of—some orchids have evolved to look and smell like bugs that will try to mate with them, and the famous corpse flower attracts insects looking for rotting meat. But in a study published in May in the journal Frontiers in Ecology and Evolution, the team found that these plants lure pollinators using a different stench of death: the smell of dead beetles. It’s 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 should be said that the flies are weird too. Phoridae, the fly family that includes “coffin flies,” are known to lay eggs in the corpses of rotting beetles. 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. “They’re really important insects that people use for forensic entomology, and here they are visiting a flower that was thought to mimic carcasses or remains,” says Anne Gaskett, a behavioral ecologist at the University of Auckland in New Zealand, who was not involved with the work. Gaskett studies how plants, mainly orchids, deceive pollinators. “It’s a beautiful match of what you might predict and what they’ve actually found.”