Carnivorous Plants Use a Smelly Trick to Catch Their Prey

Pitcher plants supplement their diets with this one strange trick: eating flesh. Usually found growing in relatively poor soil, the plants sprout pitcher-shaped cups with pretty, frilly tops that obscure their true purpose: trapping hapless insects. Look inside the pitchers and you’ll find the half-digested bodies of the plants’ victims.

How do insects wind up in this unenviable situation? Do they just, as at least one group of researchers has theorized, fall in by accident? While studies suggest that the plants’ colors and its nectar may attract prey, some scientists think pitchers’ scent may play a role as well.

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 scents seemed to be correlated with the kinds of insects that wound 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’re following.

Humans tend to describe a pitcher plants’ scent as floral or herbal, said Laurence Gaume, a scientist the French National Centre for Scientific Research and an author of the new paper. Insects may find the scent more striking. Researchers have found in the past that pitchers emitting more volatile compounds tended to attract more flies, but rigorous examinations of what exactly pitchers release and whether it’s connected to the insects they attract have been missing.

To answer this question, Dr. Gaume and her colleagues grew four different types of Sarracenia pitcher plants at their research station in Montpelier, France. They sampled the air above 39 of the pitchers, identifying dozens of volatile compounds, and sliced a number of pitchers open to sort through their contents. They also measured the pitchers’ width and depth, to see whether their shape contributed to the type of prey they caught.

Pitchers with aromas that were heavy on monoterpenes, fragrant substances known to attract pollinators, seemed to catch more moths and bees, the group found, while those emitting more fatty acids ended up with more flies and ants. Pitcher shape, too, was correlated with certain kinds of prey: Longer pitchers were heavier on bees and moths, while shorter pitchers caught more ants.

In other words, it seems unlikely that insects are just falling into a given pitcher by chance, Dr. Gaume said.

Future experiments might probe whether pitcher scents painted onto fake plants draw insects’ attention the same way, or whether altering pitcher color or shape affect the allure of the odors.

Some of the pitcher plants used in Dr. Gaume and colleagues’ research are native to North America — in fact, they can be found in the New Jersey Pine Barrens. Dr. Gaume wonders whether the same connections between scents emitted and prey caught would show up in plants grown outside of the experimental conditions of the study. She has hopes of a much larger study in North America someday to further explore these findings, with row after row of sprightly death traps, all releasing come-hither odors into the air.