Pitcher plants supplement their diet with this one strange trick: eating meat. Usually growing in relatively poor soil, the plants sprout cup-shaped cups with pretty, frilly buds that obscure their true purpose: to trap unfortunate insects. Look into the jars and you’ll find the half-digested bodies of the plants’ victims.
How do insects end up in this unenviable situation? Do they just fall in by accident, as at least one group of researchers has theorized? While studies suggest that the colors of the plants and nectar may attract prey, some scientists believe the scent of pitchers may also play a role.
In a study published Wednesday in the journal PLOS One, a research team identified odor molecules emanating from four types of pitcher plants and found that the odors appeared to be correlated with the types of insects that ended up in the pitchers. While the study is small and more work is needed to confirm the link, the findings suggest that when insects meet their deaths at the bottom of a pitcher, it may be an aroma they follow.
People tend to describe a pitcher plant’s scent as floral or spicy, said Laurence Gaume, a scientist at France’s National Center for Scientific Research and an author of the new paper. Insects may find the scent more noticeable. Researchers have found in the past that pitchers that emit more volatile compounds tend to attract more flies, but rigorous studies on exactly what pitchers release and whether it’s related to the insects they attract have been missed.
To answer this question, Dr. Gaume and her colleagues identified four different types of Sarracenia pitcher plants at their research station in Montpelier, France. They sampled the air above 39 of the jars, identified dozens of volatile compounds, and cut open several of the jars to sort their contents. They also measured the pitchers’ width and depth to see if their shape contributed to the type of prey they caught.
Pitchers with aromas heavy on monoterpenes, fragrant compounds known to attract pollinators, seemed to trap more moths and bees, the group found, while those emitting more fatty acids ended up getting more flies and ants. The shape of the pitcher was also correlated with certain types of prey: longer pitchers were heavier on bees and moths, while shorter pitchers caught more ants.
In other words, it seems unlikely that insects could fall into a particular one by chance, Dr Gaume said.
Future experiments could investigate whether pitcher scents painted on fake plants attract the attention of insects in the same way, or if changing the color or shape of the pitcher affects the appeal of the scents.
Some of the pitcher plants used in Dr. Gaume and colleagues are native to North America – they can even be found in the New Jersey Pine Barrens. Dr. Gaume wonders if the same links between smells emitted and prey captured would show up in plants grown outside the experimental conditions of the study. She hopes someday for a much larger study in North America to further investigate these findings, with row upon row of vibrant deadly traps, all releasing odors that come here.