Carnivorous plants actually get their energy from photosynthesis, just like other plants do. As you probably know, in photosynthesis plants use light energy to make sugar from carbon dioxide and water. Oxygen is a waste product. Plants make other molecules from the sugar, like starch for energy storage, or cellulose for structure.

They use the insects for nutrients like nitrogen and phosphorus. These atoms are the building blocks for proteins and other molecules. The plants break down the insects using enzymes, acids, and even little bacterial helpers. This is how we break down our food in our digestive systems. Then they absorb the broken-down molecules of their prey.

Carnivorous plants grow in places where there aren’t many nutrients in the soil. Bacteria in soil usually help break down dead plants and animals into molecules that other plants can use as fertilizer. In sandy places there isn’t much “dead stuff” in the soil. Venus fly traps do well in sandy soil. I live in Wisconsin where we have bogs that are very acidic. Bacteria don’t grow well in acidic water, so when plants die, they don’t break down quickly. Pitcher plants and sun dews grow in the bogs.

Why don’t other plants evolve into carnivores? Well, it costs the plants a lot of energy to make traps, enzymes, and acids. If there are enough nutrients in the soil, the plant is better off investing energy in reproduction and other things.

If you were a carnivorous plant, how would you lure insects into your traps?

If questions like this interest you, you may want to study plant ecology.

This is a great question! Most plants get their energy through photosynthesis meaning they just need the gasses in the air, water from the soil, and some sunlight, so why do Venus Flytraps eat insects? Well, it turns out that Venus Flytraps actually get a good deal of energy in the same way that other plants do, through photosynthesis. As you likely know, during photosynthesis, plants use the energy in the sun to drive a reaction that converts carbon dioxide and water into sugar and oxygen. The sugar produced is then converted to energy which the plants use to live, grow, and reproduce. But in addition to sugar, plants also need amino acids (protein), vitamins, and other cellular components to survive.

So where do these things come from? Well plants get most of their protein (amino acids) from nitrogen and sulfur in the soil. Phosphorous in the soil is also used by plants as a source of energy. Plants take up magnesium too as it helps their enzymes function. Does your mom every tell you to drink your milk so you get some calcium? Well, plants need calcium too which they also pull from the earth where they live. Finally, potassium is a key vitamin needed by plants as it helps regulate water movement in and out of the plant. Most plants can extract these things from the soil where they live, but Venus Flytraps are not always so lucky.

Venus Flytraps come from bogs and marshes where the soil is very acidic and minerals and other nutrients are scarce. The vast majority of plants could never survive in an environment like this because they would not get all the vitamins and nutrients and energy sources they need from the soil to grow. But Venus Flytraps evolved.

Specifically, the Venus Flytrap evolved to thrive in exactly these low nutrient environments by finding other ways to get the nutrients it needs. And that´s where the insects come in. Insects provide a great source of nutrients like nitrogen and phosphorous and carbohydrates that are missing from the soil in the typical Venus Flytrap environment.

Once an insect lands on a Venus Flytrap, the trap constricts tightly around the insect and the plant begins to secrete digestive juices, much like the ones in your stomach. These digestive juices dissolve the soft, inner part of the insect but leave the tough, outer part intact. At the end of the digestive process, which takes between five to twelve days, the trap reabsorbs the digestive fluid it let out and then it reopens, ready to catch another insect. The leftover, hard, outer shell from the now digested insect is blown away in the wind or washed away by the rain.

They don't. Venus fly traps and pitcher plants are green, photosynthetic plants that get their energy from the sun like almost all other plants.

What they need from animals is nitrogen and phosphorous, two elements that most plants get out of the soil, but carnivorous plants live in such poor soils that these elements are not available. For this reason, they digest animals using enzymes the same way carnivorous animals digest other animals, but for these plants, the main purpose in doing so is to get these necessary elements, rather than energy itself.