What if plants ate insects everywhere?

Most plants get what they need from sunlight, air, water and soil.

But some plants catch insects! What if every plant in the world caught insects?

Plants make their own food from sunlight, air and water. They also need nutrients, such as nitrogen, which most plants take up from the soil through their roots.

A few plants do something surprising: they catch insects. The Venus flytrap snaps its leaves shut, and pitcher plants trap insects in slippery cups. What if every plant, from oak trees to grass, caught insects? This thought experiment explores why carnivorous plants hunt, how they do it, and whether it would make sense everywhere.

All green plants photosynthesize, but they also need mineral nutrients, especially nitrogen, normally absorbed by roots. Carnivorous plants supplement this by trapping and digesting animals, mostly insects.

The US has five types of insect-eating plants: Venus flytraps, pitcher plants, sundews, butterworts and bladderworts. This thought experiment asks why carnivory appears in some places and not others, and what a world of carnivorous plants might look like.

Carnivorous plants live in wet, soggy places.

The soil there has very little plant food in it. So the plants catch insects to get what they need.

Carnivorous plants grow in special places, such as bogs and wet, sandy savannas. In Big Thicket National Preserve in Texas, the soil supports lush plant growth but is very poor in nutrients, especially nitrogen. Insects provide the nutrients the carnivorous plants are missing.

These plants still use sunlight to make food, like other plants. They just get most of their nutrients from the insects they catch. Four of the five types of insect-eating plants found in the United States grow in Big Thicket.

The National Park Service at Big Thicket National Preserve, Texas, explains that its soils, though they support lush growth, are very poor in nutrients, particularly nitrogen; insects supply what is missing. Carnivorous plants there photosynthesize but obtain most of their nutrients from prey.

Four of the five US types grow in the preserve: pitcher plants and dime-sized red sundews are easy to find, butterworts and bladderworts harder. The fifth, the Venus flytrap, is native only to North and South Carolina; NC State Extension says it needs wet, sandy soil and high humidity.

If every plant caught insects, gardens would be full of tiny traps.

But plants in good soil already get plenty of food from their roots.

Imagine every plant catching insects: traps on tomato plants, sticky leaves on grass, pitchers on oak trees. There might be far fewer insects around, including the bees and butterflies that many flowers need to make seeds.

But would the plants gain much? In rich soil, plants already get plenty of nutrients through their roots. Building traps uses energy and material, and a trap can only be used a few times. So for a plant in good soil, catching insects might cost more than it gives.

If carnivory were universal, insect populations might fall sharply, which could harm the pollinators and food webs that plants themselves depend on. That is an idea, not a forecast.

There are costs to consider. Each Venus flytrap leaf catches prey only two or three times before it turns black and dies (Indiana University), and traps are built to let very small prey escape, so the plant does not waste effort digesting a meal too small to be worth it. Where roots can draw nitrogen from rich soil, such costs might outweigh the benefit, which is one way to think about why carnivorous plants are concentrated in nutrient-poor habitats.

A Venus flytrap leaf has tiny hairs inside. If a bug touches two hairs, snap! The leaf closes.

A pitcher plant smells sweet. Bugs slip down inside and can't get out.

A Venus flytrap's trap is a leaf with two hinged halves and six tiny hairs on the inside. When an insect touches any two of the hairs, the halves snap shut. A chemical from the insect then switches on the plant's digestive juices, the plant soaks up the nutrients, and the leaf opens again.

Pitcher plants work differently. Sweet nectar lures insects to the rim of a tall, funnel-shaped leaf. They tumble inside, where digestive fluids and bacteria break them down so the plant can absorb the nutrients.

The Venus flytrap's trap is a modified leaf with two hinged lobes; touching any two of the six tactile hairs on the upper surface triggers closure (NC State Extension). A chemical from the prey then triggers digestive enzymes; nutrients are absorbed and the leaf resets. Toothed margins form a cage that lets very small insects escape.

Pitcher plants are pitfall traps: nectar glands lure insects into funnel-shaped leaves, where digestive fluids and bacteria break them down for absorption (NPS). The pitcher is not a perfect killer: some mosquito larvae resist its digestive juices and live in the fluid, feeding on trapped insects.

Venus flytraps grow wild in only a small part of the world, in North and South Carolina.

It is against the law to dig them up from the wild. Garden ones are grown in plant nurseries.

The Venus flytrap is one of the best-known carnivorous plants, yet in the wild it grows only in coastal North Carolina and a small part of northeastern South Carolina. Wild flytraps are threatened by building development and by poachers who dig them up.

It is illegal to collect Venus flytraps from the wild, but nursery-grown plants are easy to buy. Other carnivorous plants depend on their habitats being looked after too: in Big Thicket, controlled burns every two to three years keep the longleaf pine savannas, where pitcher plants and sundews grow, healthy.

NC State Extension describes the Venus flytrap as native to coastal North Carolina and a small area of northeastern South Carolina, and as an endangered species that cannot legally be collected from the wild; nursery-propagated stock is widely available. Indiana University's greenhouse notes that wild populations are threatened by development and poachers.

Carnivorous plants depend on specific, often fire-maintained habitats. Big Thicket's fire managers carry out prescribed burns every 2 to 3 years to maintain longleaf pine ecosystems. So the real question is less 'what if plants ate insects everywhere?' than 'how do we keep the few places where they do?'