Despite the nightmares that we all experience as we recall the man-eating plant that Seymour grew in the hit horror musical “Little Shop of Horrors,” natural selection has not yet yielded a species of plant that feeds on humans. But as humans, we sure do like to imagine the possibilities! Ever since carnivorous plants were discovered over 200 years ago, humans have created all sorts of false, all-be-it crafty, tales of trees eating humans or flesh-eating plants threatening to take over. But how exactly did carnivorous plants come to be and will they ever be a threat to humans, like Audrey II was a threat to the town in “Little Shop of Horrors?”
Plants have arguably been the most successful and long-lived organisms on this planet. So successful, that they tend to out compete each other for nutrients at times. Picture yourself as a small, low-to-the-ground, plant in a dense tropical forest. The tall trees have created quite the canopy blocking most sunlight from reaching your leaves. Other larger plants nearby have extensive root systems and water-collecting adaptations that make it difficult to acquire any drops of precious H2O. Thanks to the laws of natural selection, you realize that only the fittest of traits survive long enough to reproduce and pass on those traits to the next generation. If your species is to survive, there must be some mutations in your species that can lead to a better chance of survival. Fortunately for you, your neighbor has developed an interesting mutation–tubular, pitcher-shaped leaves. At first, this is only advantageous for collecting water, but it works for now so you reproduce with that neighboring plant and survive to pass on those traits. Years down the road, another beneficial mutation pops up in your species, the production of sticky digestive enzymes. Then another mutation pops up years later–the production of odorous chemicals to attract insects. After many years of beneficial mutations popping up in your species and subsequent reproduction and propagation of these traits, modern-day carnivorous plants were born.
When photosynthesis is not ideal due to the lack of nutrients in the environment, being a carnivorous plant is a key strategy. There is an energy cost to being a carnivorous plant (quite a bit of the plant’s overall energy budget is spent on creating digestive enzymes for example) but the insect haul that they receive generally outweighs the energy spent. Besides insects, plants have been known to spend energy to attract and capture other living things including microscopic protozoans and small vertebrates like mice. These plants don’t always attract living things to eat them, sometimes they capture insects for a brief amount of time simply to cover them with pollen. Others will attract the Hardwicke’s Woolly Bat and provide a temporary home for the bat while the bat defecates inside the plant giving it loads of nutrients.
From pitfall traps to adhesive traps and snap traps to snare traps, these carnivorous plants have developed a wide range of successful adaptations for catching and consuming prey. Check out this video for some close-up views to some of these awesome (and quite frankly, inspiring) strategies.
These plants are becoming more and more successful and multiple new varieties are being discovered each year. As Earth’s climate continues to change, there may be more and more low-nutrient environments where carnivorous plants would hold a distinct advantage. There is also something else to consider–the insect apocalypse, which is the quick decline of insect populations across the globe due to human caused events such as sweeping pesticides and climate change. The insect apocalypse would cause a negative chain reaction leading to the possible decline of carnivorous plants.
But all of these interesting facts aside, when I taught my 7th grade science class about the natural selection of carnivorous plants, most of them only had one concern, “If I stuck my hand in the plant, would it eat my hand off?” My (not so) expert answer to this question was, “No, but if you manage to fit your finger in its mouth and leave it in there long enough it would probably start to sting and VERY SLOWLY burn your skin off.” They still thought that was a cool answer. Even though man-eating plants like ‘Audrey II” don’t yet exist, it is clear that man will continue to dream and have nightmares of such a horror.
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