Anyone who’s seen the 1986 musical comedy, Little Shop of Horrors, is familiar with Audrey II. Audrey II looks like a towering, blood-eating Venus flytrap plant, even mimicking the jaw-like, snapping pod of real carnivorous plants. But while Venus flytraps consume insects, Audrey II feeds on humans. 

Thankfully, people-eating plants are fictional, says Kenny Coogan, the owner of Carnivorous Plants by Kenny Coogan, a well-known nursery in North Carolina’s Piedmont Triad area. 

On the other hand, plants that trap and digest bugs and, on occasion, small rodents are not only real, but actually quite diverse. Popular Science turned to Coogan to find out why some plants are carnivorous, while others simply soak up their necessary nutrients straight from the soil. We also asked Coogan to dig into all the details behind what makes these plants deadly, at least to birds and other small animals.

What are carnivorous plants?

Carnivorous plants are predatory flowering plants that attract, catch, and absorb animals for their nutrients. They’re both autotrophs, which are organisms that make their own food using light or chemical energy, and heterotrophs. This means that they also have to eat animal prey to survive. 

“Carnivorous plants photosynthesize,” says Coogan. “They can use the sun to convert carbon dioxide and water into sugar,” he says, for substance. “They’re just getting some extra minerals or nutrients from the bugs or the organisms that they eat.”

Meat-eating plants exist on every continent save Antarctica, and grow in sun-filled places with extremely poor, acidic, and nutrient-free soil. For instance, the bogs, swamps, and marshes of North Carolina and Florida, with their unique combination of sunlight and wetlands, allow these uniquely adapted flora to thrive. This includes Venus flytraps, which are native only to the U.S. Carolinas, and Tracy’s sundew, with its long, thread-like leaves that grow in spirals. It’s often seen blooming alongside carnivorous pitcher plants in the Florida Panhandle. 

“Carnivory is primarily an adaptation for plants to get nutrients in low nutrient environments,” says Coogan. Carnivorous plants feed on insects to obtain the nitrogen, phosphorus, and other organic nutrients they need to survive, but are unable to absorb from the soil. 

This isn’t to say that all plants that grow within poor-soil wetlands are carnivores. Take wiregrass, which is quite prominent in the southeast. “It has really heavy root systems,” says Coogan, which have formed a symbiotic or long-term relationship with mycorrhizal fungi. These fungi attach to the wiregrass roots and help them form nutrients from the region’s poor, sandy soils. 

“There’s only a certain number of niches to be filled in an ecosystem, so some plants went one way,” meaning they became carnivores, “and then some plants went the other way.”

How did carnivorous plants evolve?

There are an estimated 800 to 860 species of carnivorous plants worldwide, with new species constantly being discovered. In fact, in the more than 140 million years that flowering plants have been around, carnivory has evolved independently at least a dozen times. 

Carnivory is not inherited from a single meat-eating plant ancestor. Instead, carnivorous plants’ highly adapted leaf structures, which include sticky traps, snap traps, and pitfall traps for catching insects, have evolved and diversified more recently, largely between eight and 72 million years ago.

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Carnivorous plants are a classic example of convergent evolution. This means that unrelated lineages have all developed similar traits separate from one another to adapt to their sunny, waterlogged, and nutrient-poor environments. 

For example, “There are many different kinds of pitcher plants,” carnivorous plants that have hollowed-out pitcher-shaped leaves that act as pitfalls, says Coogan, and they’re completely unrelated. You’ve got low-growing Australian pitcher plants, which are evolutionarily closer to roses, beans, and broccoli, Asian pitcher plants that hang from tropical vines, and upright, trumpet-like North American pitcher plants. Despite their completely different DNA, they’ve all evolved the exact same, tube-shaped “pitfall trap,” says Coogan, to catch and digest insects. 

Through convergent evolution, unrelated carnivorous plants like Venus flytraps, sundews, and pitcher plants have also independently repurposed ancient self-defense genes into ingenious digestive tools. While noncarnivorous plants have long used enzymes, called chitinases, to fight off fungal infections, carnivorous plants do the opposite. They use chitinases to break down the tough, chitin-rich exoskeletons of trapped insects. This then allows them to absorb vital nutrients like nitrogen and phosphorus, transforming what were originally passive, protective enzymes into active weaponry.

Are carnivorous plants harmful to larger organisms? 

“I would say ‘no,’’ says Coogan. Almost all carnivorous plants feed exclusively on small insects like flies, mosquitoes, and spiders. 

While there are some, like giant pitcher plants, that grow large enough to trap and digest small animals like rats and shrews, “the relationship is more mutualistic,” meaning both species benefit from each other. 

Basically giant pitcher plant species produce a sweet, aromatic nectar on the underside of their pitcher lids that attracts small mammals. These mammals “sit on the lid of the pitcher plant to drink the exudate, which is a thick nectar-like substance,” says Coogan. 

They’ll often defecate into the plant while feeding, and the giant pitcher absorbs nutrient-rich nitrogen and phosphorus directly from the droppings. It’s a win-win for both parties. “And one of many examples of mutualism in carnivorous plants.” If a small animal accidently falls in, the pitcher plant will then use its acidic digestive enzymes to consume it. 

Some incredible carnivorous plants

Coogan’s favorite carnivorous plants run the gamut from small, semi-aquatic Genlisea, commonly known as corkscrew plants, to bladderwort, tiny, bladder-shaped traps that catch small, aquatic creatures and often resemble orchids. 

“There are over 200 species of them,” he says, “and they come in three different habitat types. You have fully aquatic bladderwort that are floating in water. You have terrestrial ones that live in kind of soggy soils, and then you also have epiphytic ones that are living in trees and in moss.” They all use ultra-quick, vacuum-driven suction traps to capture prey. 

In fact, bladderwort is one of the fastest predatory plants on Earth, and can suck in its prey in less than one millisecond. “The real reason I like them is because they are proliferous, meaning they flower en masse.”

Also popular: butterwarts. “Especially the Mexican butterworts or Pinguicula,” says Coogan. “The reason is that they’re excellent house plants. They look like succulents, but their leaves are sticky and they eat fruit flies and fungus gnats.” They act as a natural form of pest control.

What’s the largest carnivorous plant? 

The world’s largest carnivorous plant by trap volume is the giant montane pitcher plant. It’s endemic to Malaysian Borneo and features massive urn-shaped traps that can grow up to 16 inches tall and eight inches wide. While lizards, frogs, and birds do occasionally fall victim to the plant’s digestive enzymes and acids, most wildlife is in the clear. 

Humans can also count themselves safe, Audrey II aside. 

In Ask Us Anything, Popular Science answers your most outlandish, mind-burning questions, from the everyday things you’ve always wondered to the bizarre things you never thought to ask. Have something you’ve always wanted to know? Ask us.

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For centuries, civilizations have harnessed energy from water. However, hydropower often requires large bodies of water to move heavy machinery, confining its use to rivers. But what if the electricity needed to light up your house could be generated from raindrops hitting its roof? 

To achieve this, scientists rely on electrical charges created when materials come into contact and then separate, a phenomenon called the triboelectric effect. As an example, rubbing a balloon against your hair gives them opposite charges, causing your hair to stand up and stick to the balloon. Scientists apply the same principle to make droplet-based triboelectric nanogenerators, or D-TENGS, where raindrops slide across negatively charged surfaces. As the droplets move, their positive charges gather near the surface, freeing up their negative charges. When the droplets reach a metal strip called an electrode, these negative charges flow into a circuit, generating electricity. However, water often remains on D-TENG electrode surfaces, blocking subsequent droplets and corroding the device.

Researchers at the China Three Gorges University and the Chinese Academy of Sciences approached this problem by modifying the shape of the electrodes used in D-TENGs. They proposed that a needle rather than a strip would help droplets detach quickly, allowing charge to flow into a device that uses inexpensive components. They called this design a needle electrode droplet-based triboelectric nanogenerator, or NED-TENG.

To build the NED-TENG, the researchers prepared a plastic film using a water-repellent polymer called polytetrafluoroethylene as the negatively charged surface. They inserted a copper wire through the center of the plastic film, protruding 3 millimeters (0.1 inches) from the front side to form the needle-shaped electrode exposed to raindrops. Meanwhile, they attached copper foil to the plastic film’s backside as a second electrode, completing the circuit. The team connected both electrodes to an instrument that measures electrical performance and mounted the components on an acrylic sheet, sealing it with waterproof tape.

To simulate raindrops, the team inclined the NED-TENG at 50° from a table and dispensed tap water drop by drop from 30 centimeters (12 inches) above its plastic film. Like conventional D-TENGs, the device generated electricity as droplets slid across the film and contacted the needle electrode. However, because the water touched only a small area of the needle, it easily slid off the NED-TENG, preventing the water from building up like in D-TENGs.

The researchers then evaluated and optimized the device using 2 metrics: the force driving charges through its circuit, or voltage, and how fast its charges transfer, or current. First, they compared the NED-TENG with a conventional D-TENG. The NED-TENG generated about 564 Volts (V) and 5 milliamperes (mA) of current, nearly twice the voltage and 3 times the current of the D-TENG, and enough to power small electronics like indicator lights.

Next, they varied the droplets’ release height to maximize electricity production. They found that increasing the release height from 10 to 30 centimeters (4 to 12 inches) increased both voltage and current, peaking at about 543 V and 4 mA. At greater heights, droplets splashed hard on impact, scattering the water and disrupting the charging process they observed in sliding droplets. 

Similarly, the researchers tested different device inclination angles, ranging from 10° to 70°. Their tests revealed that the device’s electrical performance increased at steeper angles and peaked at 50°, reaching 521 V and 3 mA. At steeper angles, droplets spent less time in contact with the surface, reducing electrical output. They explained that because triboelectric materials are highly sensitive, results can vary slightly between experiments, leading to individual peak values that are lower than the highest overall outputs. 

The researchers then explored how the technology might perform in a simulated rooftop installation. To reduce power fluctuations during real-world applications, they connected multiple NED-TENGs. They observed that 10 connected devices could fill a small energy-storage component within 2 minutes and power 200 LED lights.

Overall, the NED-TENGs shed water efficiently and generated more electricity than D-TENGs, while remaining simple to build. The team noted that future upscaled studies should examine how rooftop systems can direct rainwater onto the devices at optimal heights, and how droplets interact with their surfaces to improve long-term performance. With further development, these low-cost systems could turn rooftops into practical generators powered by everyday rainfall. 

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Electric vehicles (EVs) use high-powered rechargeable batteries to store electrical energy that powers their motors. Most EV batteries use a specific mixture of metals to hold the battery’s charge, called nanoscale lithiated nickel manganese cobalt oxides, aka NMC materials. NMC materials can store a large amount of energy, making them ideal for batteries, but the metals themselves can be toxic in soil and water if the batteries are not properly recycled.  

NMC batteries leave behind a specific combination of toxic metals, so researchers can study how bacteria respond to this waste when it enters the environment. By understanding how bacteria adapt to toxic metals, scientists hope to predict how new technologies like EV batteries will affect the environment. 

In 2019, a team of researchers from the University of Minnesota reported that a common soil bacterium called Shewanella oneidensis can rapidly evolve resistance to NMC materials, but they didn’t know how. True beneficial gene evolution usually develops over thousands of generations, but Shewanella oneidensis adapted much more quickly. The team recently conducted a follow-up study to determine the genetic mechanisms behind this bacterium’s unique metal resistance.

They started by analyzing the complete DNA sequences of 33 Shewanella colonies that were resistant to either pure NMC waste or individual metals like nickel and cobalt, using a process called whole-genome sequencing. They expected to find DNA mutations in genes that control how bacteria take up and expel toxic metals that would give the resistant Shewanella an advantage in surviving NMC metal toxicity. However, they didn’t find any DNA mutations in metal-related genes. Instead, they found that a specific DNA region was duplicated 10 to 15 times in all 33 NMC-resistant or metal-resistant colonies. This result suggested to the researchers that a temporary adaptation, not true gene evolution, was responsible for the bacteria’s metal resistance. 

The researchers wanted to know more about the duplicated DNA region in metal-resistant Shewanella, so they focused on 2 gene duplication mechanisms that might serve as temporary adaptations in Shewanella. The first mechanism directly duplicates DNA regions to create extra copies of a gene, via a process called gene duplication amplification. The second mechanism moves DNA segments, called mobile genetic elements, into different DNA sections to create extra copies of a gene. 

To test whether either of these mechanisms was causing the gene duplication in Shewanella, the team grew the bacteria in different liquid media containing only cobalt, only nickel, or cobalt and nickel together. The researchers used a technique that measures the exact amount of DNA in a given sequence, called quantitative polymerase chain reaction (qPCR), to calculate how many duplicated DNA regions were in each genome sequence. They found that neither cobalt nor nickel alone triggered DNA duplication. But the bacteria grown in the media with cobalt and nickel together had 8 additional copies of the DNA region. This suggested that something about the combination of nickel and cobalt triggered gene duplication. 

To determine whether this gene duplication only occurred with nickel and cobalt, the team substituted copper and zinc for nickel in the growth media. They exposed Shewanella cells to different combinations of these metals using a grid pattern in a 96-well plate, a technique called a checkerboard assay. Then they repeated the qPCR process to measure the duplicated DNA region. They found that no other combinations of metals triggered gene duplication, suggesting that nickel and cobalt are especially toxic together, and that the gene duplication responds to this combined toxicity.

Finally, the researchers identified the function of the duplicated DNA region. They found that one of the genes within the region turned on a special protein that pushes metal ions and other toxins out of the cell, called an efflux pump protein. The team hypothesized that this efflux pump protein was responsible for removing cobalt and nickel from the bacteria’s cells. To test this theory, they grew modified Shewanella cells without the efflux pump gene in media containing cobalt, nickel, or cobalt and nickel together. They found that the modified bacteria grew well in the nickel-only treatment, but didn’t grow in the cobalt-only or combined treatments, which indicated that the efflux pump protein is necessary for Shewanella to resist cobalt toxicity. 

Based on their experiments, the team concluded that nickel and cobalt together trigger a gene duplication event in Shewanella oneidensis. This gene duplication event increases the number of efflux proteins in Shewanella that can expel cobalt and underlies its unique NMC resistance. They suggested that future researchers study temporary adaptations similar to gene duplication in bacteria to track how they respond to electronic waste and other new technologies.

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In March 2023, Southern California experienced heavy storms after almost 20 years of drought. Sixteen of these came from long, narrow regions of concentrated water vapor moving through the air, known as atmospheric rivers. During droughts, groundwater supplies up to 60% of the total water to the Greater Los Angeles area, so researchers think that stormwater from the 2023 events could have recharged groundwater reserves for future use. However, scientists lack adequate tools to assess how much groundwater is in the subsurface.

To overcome this challenge, researchers from California and Texas developed a new method to study deep groundwater. California gets a large number of earthquakes, so it has over 450 stations around the state to monitor the associated vibrations, referred to as seismic waves. To study how much the 2023 storm recharged the groundwater in the Greater Los Angeles area, the team used a tool called seismic-DI, which employs these seismic waves to estimate how much groundwater is stored at different depths. 

Seismic-DI works by measuring how fast seismic waves move through the Earth, known as their seismic velocity. The researchers explained that the Greater Los Angeles area is a very crowded city, so it produces an abundance of seismic waves. They measured changes in the seismic velocities of these underground waves to see where the groundwater is full of water, or saturated, versus partially full, or unsaturated. They used 20 years of these data to produce graphs that record changes in groundwater storage at different depths, known as hydrographs.

To validate the accuracy of seismic-DI, the researchers also compared their seismic hydrographs with groundwater thickness data from a NASA mission known as the Gravity Recovery and Climate Experiment, or GRACE. GRACE consists of 2 satellites that measure changes in Earth’s gravity, which reflect surface water and groundwater storage. Both their seismic hydrographs and the GRACE groundwater data demonstrated that the Greater Los Angeles region experienced an increase in groundwater storage from stormwater in the winter, and a reduction in groundwater storage during the dry summer. 

The team’s hydrographs showed that the 2023 storms saturated the Greater Los Angeles area groundwater down to 35 meters (114 feet), but it was abnormally dry at 200 meters (656 feet), and at a severe drought at 450 meters (1,476 feet). The GRACE data similarly demonstrated that the subsurface is in severe drought. Combined, these data indicated the 2023 storms helped the Greater Los Angeles area recover up to 90% of its groundwater at depths of 50 meters (164 feet) since the 2006-2022 drought. However, it recovered only about 40% at 75 meters (246 feet) and 20% to 30% at 100 meters (328 feet).

They concluded that the 2023 atmospheric river events recharged only shallow groundwater reserves in the Los Angeles area. As a result, they suggested future researchers consider deep groundwater reserves for a more complete assessment of total regional water deficits. While this study demonstrated that seismic-DI can successfully reveal spatial changes in groundwater and drought at depth, the team acknowledged that contributing factors like the amount, rate, and spatial variability of groundwater reserves remain targets of future work. 

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More than 90,000 tons of radioactive waste are stored on-site at nuclear power plants awaiting permanent disposal. Nuclear waste releases unstable forms of uranium and other elements, called radionuclides. Long-term exposure to radionuclides can cause cancer, so environmental safety regulations require that nuclear waste be made inaccessible for at least 1 million years. Thus, researchers are evaluating possible ways to store this waste permanently. 

One proposal is to store nuclear waste thousands of feet below ground in rock formations called deep geological repositories, or DGRs, to seal in radionuclides. Scientists can’t see into the future, so instead they look to the past to determine how well DRGs could work. A team of researchers from Canada recently analyzed uranium deposits that have existed for billions of years as an analog for how nuclear waste behaves deep underground.

Past researchers found that uranium deposits in ideal DGR conditions, with their protective casings intact, will stay contained for more than a billion years. However, these conditions require a stable geological environment. This team instead focused on uranium deposits in non-ideal conditions. They studied the Canadian Kiggavik uranium deposits, which occur in cracked bedrock approximately 500 meters (1,600 feet) below the surface. The team claimed these conditions are similar to DRGs with broken protective casings.

The team knew from previous work that most of the uranium minerals in the Kiggavik deposits are more than 274 million years old, but about 10% are less than 1 million years old. They found that these younger uranium minerals occurred alongside clay minerals surrounding the older uranium minerals and within open fractures. The researchers interpreted the older uranium as the source material of the younger uranium because of their proximity. They concluded that water must have infiltrated the deposits and interacted with older minerals, transporting uranium and forming new, younger minerals.

To determine the source of water infiltration, the researchers compared the chemistry of clay minerals formed alongside the younger uranium with modern snow in the Kiggavik region. They looked at the number of neutrons, or isotopes, in hydrogen atoms within the clay minerals, and found heavy values matching those of fresh water. These values indicated that snow or glacial meltwater was the source, rather than underlying bedrock or seawater. 

To determine when the water infiltrated over the last million years, the researchers used uranium-thorium dating to find when the radionuclides were mobilized. This dating method shows when uranium was removed from the original minerals by measuring how much its concentration was reduced by water infiltration. They found that the dates of these radionuclide mobilizations clustered into 5 separate water-infiltration events that occurred from 36 to 470 thousand years ago. 

Comparing these dates with existing climate records, the researchers found that the water infiltration events overlapped with periods when glaciers covered the ground surface. Normally, water can’t travel thousands of feet underground. But, like a hydraulic press, a glacier pushes water at its base downward. If the water encountered cracks in the ground, the pressure could inject it to the depth of the uranium deposit.

Next, the researchers wanted to measure how quickly radionuclides left the deposit. They measured the maximum distance between younger and older uranium minerals and used the age of the most recent water-infiltration event to estimate the fastest speed at which the radionuclides could have moved. They determined this maximum speed to be 0.0014 millimeters (0.000055 inches) per year. At that rate, they calculated it would take 360 million years for uranium radionuclides to travel 500 meters from a DGR at the same depth as the Kiggavik uranium deposits to the surface. This timescale far exceeds the necessary 1 million years for nuclear waste containment.

The team concluded that if glaciers were to return to Kiggavik, the uranium deposits wouldn’t experience substantial radionuclide movement, even in contact with glacial meltwater. Similarly, if a DGR has broken protective casings, radionuclides would be moving too slowly to reach the surface even if water leaked into it. They suggested their findings reduce constraints on viable DGR sites and could help ensure the long-term secure storage of nuclear waste.

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