Earthquakes knock the world out from underneath you. After a big one you realize that you’ve taken for granted the stability of your world with every step.
When you see a plant "eat" an animal, it's like a small earthquake. Watching a Venus flytrap snap up its prey momentarily upends assumptions and turns the food chain upside down. Even a seasoned naturalist like Charles Darwin found this to be true. A keen and worldly observer of nature, Darwin was spellbound by carnivorous plants. He wrote to his friend the geologist Charles Lyell about the insectivorous sundews (Drosera) he was studying and experimenting upon, "I care more about Drosera than the origin of all the species in the world." Strong words from someone who had recently published The Origin of Species, introducing the world to the concept of natural selection and evolution.
Sundews are one type of the hundreds of species of carnivorous plants in the world. There are approximately 630 species, depending on how they are divided into related or similar groups and named. Carnivorous plants are those plants that can lure or attract prey, trap and kill them, produce digestive enzymes, and absorb the nutrients from the animals as the enzymes dismantle their bodies. There are a few hundred more plants (approximately 300) that have almost all of these attributes but are considered proto-carnivorous. For example these types of plants might also attract, trap, kill and absorb nutrients from their prey but let the symbiotic bacteria living inside them do the digestion and pass the nutrients back to the plant in excreted waste. In California there are nine carnivorous plants native to the state, with a few introduced species surviving in the wild.
Not all carnivorous plants are directly related. Through generations of adaptation many completely unrelated families of plants have independently evolved their leaves into traps that are able to capture and digest animals. Some unrelated carnivorous plants look alike because their specialized trapping structures developed into similar shapes in order to capture like sized prey. Carnivorous plant trapping structures can be loosely divided into two groups, passive and active traps, with many different types of each.
Passive traps are those that capture organisms without moving to snare them. Pitfall traps, adhesive traps and lobster pot or pigeon traps are all examples of specialized leaves that passively capture.
Pitfall traps have evolved separately and diversified in many unrelated plants with widely separated habitats. While very different in origin, they all share a similar shape which is a leaf modified into a bowl or tube with liquid on the bottom. Animals that fall into the leaf drown, and then their bodies are broken down and absorbed. Pitfall traps often have distinctive patterns or nectar around their openings to lure their prey close, waxy or scaly walls to prevent climbing out, slippery fine hairs that point down, and they secrete chemicals that reduce the surface tension of water making it saturate their prey more quickly. Examples of pitfall traps include the pitcher plants in North America (Sarracenia & Darlingtonia) and South America (Heliamphora), tropical pitcher plants or monkey cups in tropical Asia, Madagascar, Australia and the islands between them (Nepenthes), Bromeliads on the mainland around the Carribean (Brocchinia), and the Albany pitcher plant in Western Australia (Cephalotus). Pitfall traps range in their size greatly, with most digesting numerous insects smaller than houseflies. Only a few grow large enough to capture small amphibians or mammals.
Adhesive traps are sticky surfaced leaves that include a toxin or narcotic to entangle and then kill the animal before releasing digestive enzymes. Small insects attracted to the glistening dew like surface become mired in mucilagenous goo. Sundews (Drosera) grow on every continent except Antartica and come in a huge range of shapes and sizes. Some have spatula shaped leaves and fit entirely on a shirt button, while others are bush sized with forking tendrils. Sundew leaves are covered with stalks tipped with glue like liquid and can curl around the trapped animal to make more leaf contact, which speeds digestion. Butterworts (Pinguicula) have fleshy flat leaves like extended tongues and are also widely spread throughout the world where small insects such as gnats will coat them like flypaper. Other adhesive trapping plants include the Portuguese Dewy Pine (Drosophyllum) and the vine Triphyophyllum (a unique plant from the Sierra Leone area of Africa that is carnivorous only in its juvenile sprouting stage of growth).
Lobster Pot or Pigeon Traps are treacherously invinting, they’re characterized by leaves that have small openings and may entice by appearing to be a comfortable shelter. Once inside, the way through the leaf twists and the bending tube like-path quickly obscures any exit. The leaves are also lined with hairs facing towards a small chamber, making it difficult to travel out. Corscrew plants (Genlisea) are native to South America and southern Africa where they grow their twisting leaves under the surface of water logged soil. Water flow in and through the leaves assists in the capture of water born organisms like insect larvae.
Active traps are the celebrities of carnivorous plants, the type that shout’s “feed me Seymour!” in Little Shop of Horrors. Their lightening quick movement dramatically traps unassuming animals in the blink of an eye, or five eyes if you’re a fly. The most widely known of these is the Venus flytrap (Dionea) from North Carolina. It has fine hairs on the inside of a pair of opposed leaves that open like a book or clam shell. When an insect crawls on the inside of the leaves it touches the hairs, triggering the leaf to shut quickly around it which squishes and kills the animal and then releases enzymes to digest it. Far less well known, the Waterwheel plant (Aldrovonda), is native to places in Europe, South East Asia, Africa and Australia. Like an underwater Venus Fyltrap, it has whorls of small snap traps radiating around a stalk that capture freshwater insect larvae or plankton such as waterfleas and copepods. Besides the snap traps of Venus flytraps and Waterwheels there are plants that use suction to pull in microscopic animals. Bladderworts (Utricularia) have bag shaped translucent leaf parts. These plants live suspended near the surface of freshwater where crustaceans like daphnia and seed shrimp take refuge. At the opening of the bag-like structure there are fine hairs that trigger the trap to pop and quickly enlarge. Any organisms in front of the bladderwort trap opening get sucked in quickly as the water rushes in to fill the void created when it enlarged.
So far only vascular plants have been observed to be carnivorous (there are carnivorous fungi). Vascular plants have tubes made of chains of cells to transport water and nutrients between specialized parts such as roots and leaves. Carnivorous plants are like all plants because they are able to grow their bodies by converting light energy and nutrients or minerals into sugars, oxygen or other molecules. Basically they make their own food (they are autotrophic) through photosysnthesis. They are able to accomplish this feat using the chlorophyll located inside their chloroplasts. While exposed to sunlight with a supply of carbon dioxide and water, chlorophyll enables a chemical reaction that makes sugars, starches and oxygen. The question most people ask when they learn that carnivorous plants can make their own food is, “why do they kill and digest animals?”
In addition to water and carbon dioxide, vascular plants require other trace minerals and large amounts of various nutrients to make photosynthesis and reproduction work. In some places like fens or peat bogs the acidity of the water can leach away available nutrients, while the enormous volume of water afforded by regular rainfall on rocky mountaintops or jungle soils can flush away those resources.
In some places there are never enough nutrients accumulated for most plants to grow. In order to live where other plants cannot, carnivorous plants have adapted their leaf structures to capture the nutrients in animals crawling or flying around them.
In California, spring water flowing across sunny exposed rock creates a habitat where plants thrive. However, on serpentine outcrops, the same type of rock has very few of the minerals that plants need to flourish. A few carnivorous plants like sundews, butterworts, or pitcher plants take advantage of their ability to get nutrients from insects to be able to colonize and reproduce where other plants can’t.
Because carnivorous plants are specialized to live in habitats where other plants cannot, they are especially vulnerable to extinction if those rare habitats are damaged or destroyed. Invasive species and habitat destruction account for most recent extinctions, and both severely limit the types of animals or plants (the biodiversity) that can live in an area.
Carnivorous plants also suffer poaching. Many of these singular plants are slow growing because of the limited nutrients around them. They can’t grow or reproduce fast enough to keep pace with people cutting or stealing them from the wild. Because carnivorous plants are often sold as novelties and take years to grow to a size suitable for sale in a nursery, they command a comparatively high price. This makes them attractive to people who want to avoid the effort required to raise them, stealing from the wild to make a quick profit. For example, Venus Fly traps, which only grow within a 75-mile distance of Wilmington, North Carolina, require about 3 to 5 years of growth before they become big enough to sell. These plants easily sell for $3.00 to $20.00 each. In a few hours one person can fill a duffel bag and poach more than 1,000 plants from a park or preserve. This devastates a wild population of plants and causes severe damage to marshy bogs or fens due to digging. To combat the damages of poaching, local and international laws restrict shipment or sales and arrests of poachers are publicized.
On a positive note, plant nurseries have collaborated to reduce the cost, time and challenges to growing Venus flytraps. This effort has reduced the pressures on wild plants by dramatically increasing the supply of Venus Flytraps for sale and lowering the market price, which in turn reduces the incentive to poach them. And yet, even with these efforts poaching still occurs, and some species of carnivorous plants are still extremely difficult to propagate out of the wild.
Plants that eat animals are a novelty, fascinating to most people and almost all children. For this reason they are a sensational prop for engaging students and explaining a variety of natural science concepts. Successfully raising carnivorous plants in a classroom or home setting requires that the caretaker learn about the special needs of that species and try to recreate the conditions of their preferred habitat— it’s rewarding, but never easy.
Bay Area Carnivorous Plant Society www.bacps.org
Barry Rice, Growing Carnivorous Plants Peter D’Amato, The Savage Garden
San Francisco Conservatory of Flowers University of California Botanical Garden (Orchid and Fern House)
Cactus Jungle Nursery and Gardens, Berkeley, CA, California Carnivores, Sebastopol, CA, Predatory Plants, Half Moon Bay, CA, Plant’It Earth, San Francisco, CA, Bay Area Carnivorous Plant Society annual show and sale, location varies, The Pitcher Plant Project, San Francisco, CA, seasonal sales http://thepitcherplantproject.com
Joseph Kinyon believes curiosity is a skill and is grateful for opportunities the natural world provides to hone that skill. He makes maps to pay the rent.