Some have teeth, some a sticky, entrapping liquid. Others have one-way tunnels leading to pools of digestive juices and are said to exude a paralyzing perfume. All of which are good reasons to beware in the vicinity of carnivorous plants – if you’re an insect, that is, or maybe even a slug or worm. Anything larger is mostly safe from the specialized adaptations that sundews, pitcher plants, and bladderworts, the most common carnivorous plants in Vermont and New Hampshire, have evolved to obtain nutrients in the impoverished, acidic wetland habitats they inhabit.
Unfortunately for curious naturalists, the one with teeth (really modified leaf margins) – the Venus flytrap – is not found in the wild around here. The less well known but truly beautiful sundew, which is found in this area, also uses its leaves – evolved into red, glistening paddles in a feat of evolutionary ingenuity – to nab passing insects. Sundews are named for their “sparkle,” really tiny droplets of moisture exuded by this diminutive plant’s leaves. This moisture is not benign dew, as the name suggests, but sticky mucus that attracts the attention of passing insects who then approach, usually too close, to investigate. Once the insect makes contact with the mucus, it is trapped, and the sundew’s tentacle-like, modified leaf curls inward to smother and begin digesting it. The resulting insect slurry is then absorbed by special glands on the leaf’s surface.
Pitcher plants, too, slowly digest their insect prey, albeit within a pool of juice that breaks the insect down into its nutritional components. Instead of advertising with sparkling dewdrops, pitcher plants instead emit an attractive perfume. Like the cartoon dog drawn to a freshly baked pie on a ribbon of scent, an insect is lured ever closer to a pitcher plant’s pitchers, also modified from leaves. Lured by the promise of sweet nectar, an insect ventures heedlessly into the pitcher’s depths. Alas – once inside the entrance, the hapless fellow has taken his last steps; he may realize his folly and attempt to climb or fly out, but the downward-pointing hairs, waxy coating, and snug entrance to the pitcher will defeat his efforts until, exhausted, he falls into the pool and is slowly absorbed. Frogs will often perch at pitcher entrances, hoping for an easy meal; the predator becomes the prey on occasion, as evidenced by frog skeletons found in pitchers by prying botanists.
The last of our common carnivorous plants, the bladderwort, is by comparison an accidental consumer. No dew, no fragrance, just chance – although some scientists speculate that the sugary mucus this plant excretes may in fact attract prey. Bladderworts form tangled, floating mats on the surfaces of water bodies, full of thousands of nearly invisible, bladder-like appendages. Each bladder maintains a negative pressure inside, such that its walls are slightly indented. At the flap that seals the bladder shut, pointy hairs thrust into the water, and when microscopic insects and animals brush the hairs, the bladder door is triggered to spring open. Water rushes into the bladder as the inside and outside pressures equalize. The door snaps shut again, and any tiny prey that have been sucked in swim around until they run out of air, food, or both, at which time natural decomposition breaks them down for the benefit of the bladderwort.
While these three hardy, insect-eating plants may seem to have cunning, premeditated feeding methods, their actions are truly just an evolutionary product of their environment: acidic waters, such as those found in bogs. Bogs are a specific sort of wetland with very low nutrient levels. Pitcher plants, sundews, and bladderworts lend life to an otherwise low-diversity wetland, but to live, they must reap an unconventional source of nutrients. To do so, they have sacrificed deep roots and highly photosynthetic leaves – truly a risky tradeoff since, like all green plants, carnivorous plants attain vital carbohydrates from photosynthesis. The insects serve as a reservoir of nutrients normally found in soil but lacking in acid waters, such as nitrogen and phosphorus.
Unfortunately, many of our bogs and other wetlands are being lost to construction activities and other causes of wetland draining. Increasingly, carnivorous plants are forced to live in ever smaller “islands” of suitable habitat. Someday, they may not be as easy to find, or to marvel over, or to remind us that not all plants follow convention.
To find members of this odd trio, look no farther than your nearest bog or other acidic wetland. Land trusts and conservancies are especially interested in wetland conservation, so check with your local outfit first. A good starting point is The Nature Conservancy. Or you can try the Upper Valley Land Trust’s list of conserved areas.
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