Carnivorous Plants Use a Smelly Trick to Catch Their Prey

Pitcher plants eat flesh as a way to supplement their diet. The pitcher plants are usually found in poor soil. They produce pitcher-shaped cups that have frilly tops to hide their true purpose, which is to trap insects. You can find half-digested victims of the plants inside the pitchers.

What causes insects to be in such a bad situation? They just fall in, as one group of scientists has suggested? Some scientists believe that pitchers' scent could be as important to attracting prey as the colors of the plant and its nectar.

A research team published a study in PLOS One on Wednesday that identified the odor molecules coming from four different types of pitcher plants. They found that these scents were correlated to the type of insects that ended up in the pitchers. The study was small, and further research is needed to confirm this link. However, the findings indicate that insects may follow an aroma when they die at the bottoms of pitchers.

Laurence Gaume is a scientist at the French National Centre for Scientific Research, and the author of this new paper. He said that humans tend to describe the scent of pitcher plants as floral or herbaceous. Insects might find the scent more appealing. Researchers found that pitchers with more volatile compounds attracted more flies. However, they have not examined the exact chemicals released by pitchers and if this is connected to the insects the pitchers attract.

Dr. Gaume, along with her colleagues, grew four types of Sarracenia pitchers at their Montpelier research station to answer this question. The researchers sampled the air over 39 pitchers to identify dozens of volatile chemicals, and then sliced open a few pitchers to examine their contents. The researchers also measured the width and depth of the pitchers to determine if their shape affected the prey that they caught.

The group discovered that pitchers emitting monoterpenes - fragrant substances known to attract insects - attracted more bees and moths. Those emitting fatty acids, however, attracted more flies, ants, and other insects. The shape of the pitcher was also correlated with prey types: longer pitchers attracted more bees and ants, while smaller pitchers attracted more flies.

Dr. Gaume explained that it is unlikely insects just happen to fall into a pitcher by accident.

Future experiments could test whether the scents of pitchers applied to fake plants attract insects in the same manner, or if the pitcher's color or shape alters the attraction.

The pitcher plants that Dr. Gaume used for his research and those of her colleagues are native North American species. They can even be found growing in the New Jersey Pine Barrens. Dr. Gaume wonders if the same correlation between scents released and prey captured would appear in plants grown outside the experimental conditions of this study. She hopes to see a larger study conducted in North America one day, which will include rows and rows of death traps that emit come-hither scents.