Mad About Science

Carnivorous plants

By Brenden Bobby
Reader Columnist

Carnivorous plants are a curiosity of the natural world. Most plants are stationary and docile, presenting very little threat outside of the occasional falling tree or poisonous berry. Then there is the Venus flytrap, a horrifying little bit of flora that eats insects alive. How can a stationary plant be an alpha predator, and more importantly: Why?

The “why” behind floral carnivory is one of the clearest answers scientists have regarding the enigma of carnivorous plants. Plants need nutrients to survive, and if plants can’t get all of those nutrients from the soil, then they have to figure out a different way to procure those nutrients. 

The common thread between all carnivorous plants is that they exist in nutrient-poor environments and create specialized adaptations to counteract those conditions. If the plants were growing in soil with more phosphorus and nitrogen, they wouldn’t produce as many specialized leaves for catching insects. 

This is often seen by amateur botanists that transplant a store-bought Venus flytrap into rich potting soil. The plant may appear to be dying, but it really realized it doesn’t need so many traps anymore, and will instead produce more photosynthesizing leaves, because carnivorous plants still need photosynthesis to survive — just like any other plant. However, their specialized leaves (while often green) don’t actually photosynthesize sunlight like their other leaves. In their natural environment, carnivorous plants have to balance their resources very carefully in order to survive.

The most recognizable type of carnivorous plant is the Venus flytrap, but this isn’t the only form of carnivory found in the plant world. Pitcher plants grow throughout the world, including a wide variety in North America. These have specialized leaves called pitfall traps that act like a well. They form a hollow structure like a pitcher that is partially filled with digestive liquid designed to drown and digest insects that fall into the plant’s leaf. These pitfall traps have myriad methods for luring insects. Some utilize ultraviolet coloration patterns while others use an aromatic nectar that also makes the brim of the leaf slippery.

These types of plants frequently use substances they produce to attract and entrap prey. Sundews are particularly diabolical, creating long and colorful stalks lined with glands and little tentacles that secrete a sticky mucilage. The sticky substance is sweet and attracts insects like flies or beetles, which become trapped by its stickiness. The mucilage acts not only as an attractant and trap, but also a digestive enzyme that breaks down the body of the prey to create a nutrient soup that is consumed by the plant through specialized sessile glands.

Native to South Africa, the cape sundew has a mechanism that mirrors the action of more aggressive plants like the Venus flytrap. Insects triggering individual hairs on the surface of the plant cause its leaf to curl and wrap around its prey, absorbing the maximum amount of nutrients from the entombed insects. This is a mechanism called thigmotropism, which is also seen in vining plants like beans or grapes. This is the plant altering the direction of its growth in response to physical stimuli, particularly touch.

Waterwheel plants also use this mechanism, and are the only known aquatic species of carnivorous plant to employ this method of snap trapping. Their trapping leaves are quite small and best suited for capturing very small marine invertebrates.

Snare traps, such as South Africa’s corkscrew plant, are ingenious tricksters that create an elaborate root structure to entice single-celled organisms to enter the roots and feast, only to be guided down through the plant’s roots by hairs that send the organisms into digestive bladders to be broken down and consumed. The way this occurs very closely mirrors human fish traps using a narrow opening lined with sharpened sticks to dissuade fish from trying to escape the trap.

Suction traps exist in aquatic environments and have a more complex trapping structure than snares. Suction traps such as bladderwort are rootless, but have specialized sensors near the mouth of the trap that detect the presence of moving prey. When the prey is close enough, it bursts an air bladder on the inside of the plant to create negative pressure that pulls the prey in as well as sealing a trapdoor mechanism at the same time. The mechanism seals shut with a slimy secretion and the prey is digested while trapped inside the plant.

Not all carnivorous plants are killers. Low’s pitcher plant cuts to the chase, not wasting resources on trapping, killing and digesting prey. Instead, it attracts the mountain tree shrew with sweet nectar. The tree shrew will feast on the nectar and, while doing so, it poops into an opening in the plant that then digests the nutrient-rich waste. Comically, this plant’s specialized leaves look somewhat like a toilet.

Are you curious about cultivating carnivorous plants of your own? Many of these plants are often very beautiful additions to any home, while also helping rid your space of a few common pests. You can check out books about carnivorous plants from the library, found in the nonfiction section filed under 635.9 in the Dewey decimal system. That’s downstairs, behind the information desk and to the left in the Sandpoint library. Hit the Teen Zone and you’ve gone way too far.

Stay curious, 7B.