Compared to Venus flytraps, which clamp their jaw-like leaves around flies and other small, wriggly bits of prey, the various pitcher plants in existence must seem like pretty benign carnivores. Their way of capturing prey strikes me as a bit like windmill fighting: can they help it if juicy insects and ripe-looking amphibians happen to tumble into the pits of digestive enzymes waiting at the bottom of their pitcher-shaped leaves?
In fact, pitcher plants don’t consume every organism that ends up in the pit. Some of those organisms actually help pitcher plants process the other creatures they’re about to eat, somewhat like parents who cut their children’s food for them, though slightly more savage.
Nepenthes is a genus of pitcher plant found primarily in the southeast Pacific. Each leaf starts with a thin tendril at the tip, then inflates like a long balloon until finally, at maturity, a flap of leaf material at the tip opens, and a pitcher is formed.
Pitchers in general are excellent for holding liquid, and those belonging to the plants of genus Nepenthes are no exception, though the sweet, attractive nectar and the digestive enzymes that they produce differ substantially from the iced tea you might pour yourself on a hot summer day.
As effective as the digestive juices that Nepenthes make (capable, in some species, of taking out entire mice) are, the digestion process can always stand to go more quickly. Some Nepenthes have tiny hollow chambers in their stems where ants can make their homes. Instead of falling into the pitchers, the ants snag other insects attracted by the nectar. The ants are sloppy eaters, which is a good thing for Nepenthes, as the stray insect crumbs slip into the pitcher and get digested much sooner than an entire insect would.
So some ants and some pitcher plants make good matches. Others, not so much. Sarracenia is another genus of pitcher plant; some of its member species grow from the grounds of peat bogs in North America (including Illinois’ own Volo Bog). A Sarracenia‘s pitcher looks different from that of a Nepenthes, in part thanks to a flange running the length of the leaf that creates a stream of nectar. Ants climb the leaf and follow the trail, which leads to the edge of the long, tall pit, and—whoops, in they go.
That’s not to say that Sarracenia species can’t play nicely with others. The larvae of some insects, such as the blowfly, live inside the pitcher and feed on partially digested remains, while bacteria in the water that also collects in the bottom of the pitcher help get that digestion going in the first place.
Though they pose a threat to some living creatures, pitcher plants hardly are isolated organisms, at least within a habitat. In the case of Nepenthes, our evolutionary tree suggests otherwise, as Nepenthes are believed to exist much in the same form that they have for millions of years. In other words, the Nepenthes genus has no close relatives.
That’s okay, little pitcher plants. At least the ants seem content keeping you company.