Nature Notes: Hungry Plants
We all know about the Venus flytrap. It’s a carnivorous plant that lives sparingly in the coastal Carolinas and catches insects in its trap. How many of us, however, know that right here on the East End we have more than a handful of such plants, which eke out a living by catching and eating insects.
Depressions in dunes that fill with native groundwater for part of the year are favorite places for a bunch of flowering plants that are not only attractive but unique in other ways. They have carved out niches in spots with very low mineral contents where flowering plants that require nitrogen, phosphorous, potassium, magnesium, and other natural elements would have a hard time getting started.
It’s not that these unique pothole plants don’t require nutrients; they have evolved very special ways of acquiring them — in many cases, not from the water or wet soil they reside in, but from the air surrounding them. They attract insects, trap them with sticky hairs or cups of liquid, then digest them in the same manner as animals digest their foodstuffs, with specific enzymes and catalysts.
These are the insectivorous plants of science fiction movies and books, but, unlike in the movies, they are not capable of ingesting a human or anything much larger than a horsefly. They get by winningly on the small stuff, especially that which they can attract with colors, odors, or other enticements.
Long Island is not known for its rich flora, say the way inland areas like Appalachia are, but it has its share of unusual insectivorous plants, particularly because its glacial, Aeolian, and wave-washed soils are, for the most part, lacking in essential plant nutrients.
The largest of the carnivorous plants is Sarracenia purpurea, the purple pitcher plant. It has red-purple flowers and spiraling conic leaves. The tips of the leaves are wet with a slippery fluid that not only attracts insects but also slides them down the inner column of the leaf into a vat of digestive fluids mixed in water. Very few insects that land on the edges of the leaves make it out alive.
You can find a bunch of them in the bogs off Route 51 in the Town of Southampton. While the pitcher plant is death to intruding insects, it is a home to myriad rotifers, midges, protozoans, and other so-called inquiline micro-organisms that commune in the wetness and share the bounty from the digestion of befallen insects.
There is one insect with wings that makes it in and out of the pitcherplants’ pitchers with ease. It is the pitcher plant mosquito, Wyeomyia smithii. In fact, it trusts its host so much that it deposits its eggs in the pitcher’s water, just as the mosquito that bites you at home lays its eggs in an old tire, can, or fish pond. The larvae hatch from eggs, feed on the smaller organisms swimming around, and eventually morph into adults that aren’t normally sanguineous — the female doesn’t require a blood meal in order to lay fertilized eggs. Thus humans, other mammals, birds, reptiles, and other critters are not bothered by it except in a few areas around Arkansas and Texas at the bottom of its range, where it can look for blood before depositing a second egg crop.
Closer to home are the three species of sundews that reside on the North and South Forks. They also have pretty-colored diminutive flowers and leaves covered with fine glandular hairs that stick to and close on any insect that lands on them. There are two sundews with normal-looking leaves except for the thick covering of reddish glistening hairs — the round-leaved sundew and the spatulate-leaved sundew. The third and most spectacular of the three is the thread-leaf, so called because its leaves are erect, longish thin cylinders, not at all leaf-like, but covered with the same glistening reddish hairs. The flower stalks get to be six inches tall and so, in a way, the thread-leaf has a decided advantage over it smaller cousins.
All three can be found occupying the same square foot of damp soil, however. Perhaps it is a case of “the more the merrier,” in other words the more glistening red hairs, the more likely that flying insects will be drawn to them.
There is a third group of carnivorous plants residing locally. They tend to be aquatic or subaquatic and are called bladderworts. You can find them in Scoy Pond, Crooked Pond, and, in fact, almost any longstanding freshwater pond around that is low in nutrients. Some are floating, like the purple bladderwort; some, like the horned bladderwort, are anchored to the substrate below.
All of these bladderworts have little “catch-’em-alive” traps, or appendages, with “teeth” that close around the aquatic insects that wander into them. Like the lobster trap or crab pot, there is no practical way out once inside. They also have colorful flowers that can rise above the surface of the water. Almost all flying insects are attracted to pretty flowers.
In terms of numbers, the pitcher plants have the fewest species, only three altogether in North and South America. The sundews are more common, with almost 190 different species. Utricularia, or bladderworts, are the most common, with well over 200 species, and are found on every continent except Antarctica, maybe because two-thirds of the earth’s surface is water.
Long, long before the era of fancy outdoor optical instruments for viewing nature, some sharp naked eyes set in patient immobile frames were able to tell that the little sundews and their brethren trapped insects. It was Charles Darwin who had the patience in the 1860s to sit and watch sundew for hours until an insect landed on one, moved, and those glistening hairs fenced it in. His book published in 1875, “Insectivorous Plants,” started an entirely new field in botany, and served to support his theory of natural selection.
Apparently, insectivorous plants evolved from several different plant groups and most likely are still evolving today. One wonders, however, with all the nutrients available in the world’s thick blanket of atmospheric pollution, if evolution in these plants will begin to turn around and proceed in the other direction.