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Nature News

How a pitcherplant catches its dinner

by Sue Pike The York Weekly/Portsmouth Herald/Foster's Daily Democrat

I experienced the exhalation of nature last week.  I was in a bog in  Farmington NH, crouched down low over a patch of brilliant scarlet and chartreuse pitcherplants, trying to take photos into their water-filled orifices (yes we had just had rain for the first time in a long time!) in the hopes of catching one of these carnivorous plants slowly consuming some luckless insect.   My camera lens kept fogging up and I realized it was caused by condensation of the water vapor evaporating out of the pitcherplant---not a true exhalation, but something close.

 Because of the drought I was able to walk out into the bog, much further than I normally would have without hip waders. While the soil still held enough water for the ground to be damp, it lacked its normal squishiness-the water level should be near the surface in most bogs, in the midst of a drought it is not (the term “bogged down” comes from that sensation of sinking up to one’s knees in a bog, hard to move while embedded in the muck).  

This bog was covered with a thick layer of sphagnum moss, a characteristic of most bogs.  The sphagnum moss acidifies the environment in which it lives, making it difficult for most plants to thrive—only hardy, acid-tolerant plants can flourish, plants like blueberries, cranberries, cotton grass and carnivorous pitcherplants. Pitcherplants were there in abundance, nestled in amongst the cranberries and marsh grasses, splashes of color with their bright green and red pitchers, sprouting flowers that nodded red and yellow from tall, straight stalks

The only pitcherplant native to New England is the purple pitcherplant (Sarracenia purpurea).  Pitcherplants have hollow, pitcher-shaped leaves (hence the name) that collect water and trap insects.  The pitcherplant needs these insects to provide nutrients that are unavailable in the acidic peat (partially decomposed plant-rich soil of the bog).  The inside of the pitcher is lined with downward-facing hairs that help prevent prey from climbing out of the pitcher (not too efficient though-it is thought that less than one percent of flies that fall in are actually trapped).  Once trapped, the insect eventually dies and is broken down into usable nutrients by the host of insects and microorganisms that live in the pitcher. 

There are worlds within worlds in these pitchers; “At least two insects also use the pitchers as a breeding location. A community of microorganisms eventually develops in the water at the base of the pitchers. These microorganisms live on the nutrients of the decaying insects, and may actually increase the nutrients available to the plant by further digesting its prey. The microorganisms are themselves prey to at least two species of carnivorous insects – the larvae of a mosquito and the larvae of a midge – which complete their life cycles in the pitchers. For some reason, the digestive enzymes secreted by the plant affect neither species.” (U.S. Forest Service).

The flower of the pitcherplant is also unusual.  The deep red color is thought to attract pollinating flies by resembling raw meat.  The round, enlarged ovary sprouts a large, upside-down umbrella that acts as a landing platform for pollinators.  This landing platform is surrounded by the pollen-producing anthers and because of this arrangement is laden with pollen.  In addition, the ovary drips nectar onto the platform—pollinators land and walk around sucking up the nectar and picking up pollen in the process.

Carnivorous plants haunt our imaginations because, by relying upon prey (instead of sunlight) for some of their energy needs, they represent a link between plants and animals, they somehow feel (to me) like close cousins.  I like to walk out onto a bog, see them there lying in wait and say hi.