How much do carnivorous plants differ from the rest of the plant kingdom? You might have found yourself wondering at one point or another whether carnivorous plants photosynthesize – after all, if they digest insects to get the proper nutrients, do they need the energy that comes from the sun in the first place?

Today on HerbSpeak, you’ll learn more about carnivorous plants than the average joe, discovering their likeness (and differences) between them and “regular” plants that don’t display any carnivorous behavior.  

What Is Photosynthesis?

Before we dive into the “meat” of the article, let’s first cover our basis so you understand the process of photosynthesis and how it’s valuable to plants to begin with.

Ultimately, photosynthesis is a process utilized by many plants, bacteria, and algae that requires three basic ingredients to be successful: sunlight, carbon dioxide, and water.

Plants produce a green pigmentation called chlorophyll which allows the plant to synthesize food that helps keep it going.

This chlorophyll is often in great enough amounts to color parts of the plant green – particularly the leaves and stems where photosynthesis primarily takes place – but other pigments, or blends of different pigments, may be present in high enough quantities to make it appear a different color to us despite still containing some quantity of chlorophyll.

In other words: the green part of the plant is the primary part that needs sunlight, but most plants can perform some degree of photosynthesis in all pigmented parts except the roots.

The photosynthetic process occurs as a reaction primarily between carbon dioxide and water. The process is then initiated by sunlight.

Within the plant, water is oxidized, which causes it to lose electrons, and the carbon dioxide begins to gain the electrons the water loses. This results in the water transforming into a byproduct we are indebted to, called oxygen.

This process transforms carbon dioxide into the intended product that will help fuel the plant in all other functions: glucose.

Essentially, this process transfers the energy from sunlight into chemical energy that the plant can later disperse as needed to help it perform other metabolic functions like growing, flowering, seeding, and transferring nutrients.

Since plants do not eat, and they depend on sunlight to produce their own energy, it makes sense to wonder if carnivorous plants need such a function as well. After all, if these plants do consume and eat, would they need to depend on soil nutrients and sunlight at all?  

Do Carnivorous Plants Photosynthesize?

Yes, carnivorous plants are like most other plants in that they do, in fact, photosynthesize. They may be alien to their plant cousins when it comes to dietary choices, but that doesn’t make them any less of a plant.

Carnivorous plants have just a great a need to manufacture glucose as other types of plants; this glucose can be used to create starches and cellulose that are essential to the plant’s growth, structure, and survival.

Likewise, proper glucose manufacturing through photosynthesis will allow the plant to easily adapt to changes in the environment, fight off predators and diseases, continue growing, and transport nutrients efficiently.

Without these processes, the plant would not survive whether it was carnivorous or not. This process and its resulting manufactured chemicals are critical to any plant’s basic metabolic functions.

It is true, however, that in many carnivorous plants, the development of traps has led to a decrease in its ability to photosynthesize. (1) After all, when most of the photosynthetic activity occurs in the leaves, where the stomata are located, it is difficult to modify leaves for a separate purpose. This predicament has led to some interesting developments in the evolution of carnivorous plants.

[…] traps contribute little to the, already comparatively low, photosynthetic performance of carnivorous plants. In pitcher plants this conundrum is solved either by spatial separation (insect and light-trapping functions in different parts of the leaf) or by temporal separation (the production of two distinct leaf types).

Chris Thorogood

Ultimately, while carnivorous plants seem to have the odds stacked against them, particularly where soil nutrients are concerned, you can see the effects of their evolution even beyond their traps.

Photosynthetic ability is portioned to different parts of the leaves or on separate leaves entirely, and most plants grow short and stout. For carnivorous plants with stems, these stems are often long and thin, maximizing the amount of growth they can achieve on as minimal resources as possible.

Why Do Carnivorous Plants Eat Insects?

Carnivorous plants typically need insects to survive because the soil nutrients are poor enough where they are growing that it is inhospitable for other plants.

Over time, this led to the evolution of carnivorous plants, which expend great amounts of energy on trapping prey – whether it’s insects, small amphibians, or mammals – in exchange for their nutrients. It is the perfect example of a cost-benefit analysis and adjustment in the natural world.

Through the production of digestive juices, these plants break down their prey into a form that the plant can absorb more readily, allowing it to benefit from the nutrients that it is otherwise missing from the soil around its roots.

So, what are these carnivorous plants after?

Why do carnivorous plants eat insects and invertebrates when they would get the nutrients from the soil?

Well, the answer is easy when you consider the conditions that most carnivorous plants live in: poor-nutrient soils, notably lacking in phosphorus and nitrogen which are essential to plant development and survival.

Where Do Carnivorous Plants Live?

Most carnivorous plants live in bogs and wetlands, often in sandy or acidic areas.

It is also important to note that not all carnivorous plants are terrestrial; there are some semi-aquatic or fully aquatic plants that are carnivorous as well. Most notably, and most overlooked, is the bladderwort, which is commonly found floating in ponds and bogs, feasting on tadpoles, insects, and small invertebrates.

In these areas, it is difficult plants and bacteria to grow. Acidic environments, like those found in some bogs and wetlands, cannot support as much bacterial break down as more pH neutral environments can. (2)

Carnivorous plants are mainly restricted to sunny, moist and nutrient-poor environment, because only in this environment would the cost of producing traps be lower than the benefits gained from prey.

Andrej Pavlovic

This means that any decaying plant or animal matter that would otherwise get broken down into the soil isn’t broken down in a short enough timespan to support the plant. 

In sandy areas, the bacteria that is present in normal soil to help break down all the organic material just simply aren’t present – or aren’t present in high enough quantities – to make a meaningful change to the soil system around the plant’s roots.

These are both examples of nutrient-poor soils that are not supportive of most plant life, as the plants remain in one place for the duration of their life and rely on the nutrients around their roots to help sustain them.

Over time, plants evolved proto-carnivorous and fully carnivorous behaviors to compensate for the lack of nutrients. Namely, the nutrients that the plant is seeking when it kills and digests its prey is nitrogen and phosphorus – nutrients that would be bountiful in healthier soils.

The development of traps and digestive functions allows these plants to capture prey that contains the nutrients they are missing from the soil and digest them into a form that can be easily absorbed by the plant.

This, in turn, allows these carnivorous plants to thrive natively in areas that could not otherwise be filled. In the natural world, if there is an opportunity for a plant to further its species, it’s not long before it develops mutations to take advantage of the environment.

  1. Chris Thorogood, Shedding light on photosynthesis in carnivorous plants.,
  2. Andrej Pavlovic, Spatio-temporal changes of photosynthesis in carnivorous plants in response to prey capture, retention, and digestion,