Can Venus Flytraps catch flies? What misunderstandings do you have about carnivorous plants?

"Tropical Life, Beautiful Yearning" - "Can Venus Flytraps Catch Flies?"

——What misunderstandings do you still have about carnivorous plants?

Everything has a soul, except mosquitoes and flies. No matter from which angle you look at them, they are annoying insects.

In order to sleep well at night, humans have developed various solutions. Among them, using insectivorous plants including Venus flytraps to reduce indoor mosquitoes and flies seems to be an environmentally friendly and high-end option.

But is it really possible to buy a Venus flytrap and place it indoors? What other misunderstandings do we have about carnivorous plants?

Image source: Visual China

Will carnivorous plants starve to death if they cannot catch mosquitoes and flies? No.

To make this clear, we also need to explain why animals will starve to death if they don't eat.

Whether it is animals or plants, they need two major types of supplies to survive, one is matter, and the other is energy. The growth of organisms is like building a house, which requires bricks and tiles (matter) and the energy required to build a house with bricks and tiles. "Bricks and tiles" include various elements, such as carbon, hydrogen, oxygen, nitrogen, sulfur, phosphorus, potassium, iron, etc. These elements will combine with each other to form water, protein, fat, sugar, vitamins, carbon dioxide and various inorganic salts, so in many cases, organisms obtain "bricks and tiles" by absorbing these compounds. For example, proteins and some inorganic salts contain a large amount of nitrogen, phosphorus, potassium, sulfur and other elements. At the same time, compounds such as fat, sugar, protein, etc. also contain a lot of energy. Therefore, for animals, eating these things into their stomachs will get both "bricks and tiles" and energy.

But plants are different. There are not many fats, sugars, proteins and other energy-containing substances in the soil for them to absorb. They can only absorb water and inorganic salts from the soil, which are only used as "bricks and tiles" but do not contain energy. In addition, plants absorb carbon dioxide from the air through their leaves to obtain carbon and oxygen, two important "bricks and tiles".

So where does the energy for plant growth come from? It is obtained from sunlight through photosynthesis. Therefore, light is vital to the survival of most plants.

It can be seen that if animals do not eat, they will not get any "bricks and tiles" and energy, and will starve to death. Without light, plants will lose their energy source and will "starve to death" over time. However, there are exceptions. Some special plants will parasitize other plants. Their roots can directly absorb all the "bricks and tiles" and energy from the host's body. Therefore, these parasitic plants can survive without sunlight, just like animals.

Schematic diagram of the sources of animal and plant survival supplies

But carnivorous plants are not parasitic plants. They contain chlorophyll like ordinary plants, which means they cannot live without sunlight. Carnivorous plants prey on small animals just to absorb some non-energy substances in their bodies, such as nitrogen. Nitrogen is an important "brick and tile" for plants. If the intake is insufficient, it will affect the growth of plants. Therefore, many plants will come up with various ways to supplement the lack of nitrogen in the soil. For example, like soybeans, symbiosis with nitrogen-fixing bacteria is one of the methods. Nitrogen-fixing bacteria can absorb nitrogen from the air and convert it into nitrogen-containing inorganic salts for plants to absorb.

The soil where carnivorous plants grow is usually not rich in nitrogen. Therefore, carnivorous plants often use the method of preying on small animals. Generally speaking, insects and other small animals are rich in protein, and when the protein is decomposed, a large amount of nitrogen will be released. At the same time, small animals also contain a large amount of inorganic salts such as phosphorus and potassium. Therefore, preying on animals can obtain a wide variety of nutrients.

However, carnivorous plants do not have the ability to directly absorb nutrients containing energy from their prey. Their energy source is still sunlight. If carnivorous plants do not eat, they will only lose some of the "bricks and tiles" such as nitrogen and phosphorus, and will not fundamentally cut off the source of "bricks and tiles" and energy, because the roots can still absorb some inorganic salts such as nitrogen and phosphorus from the soil. Therefore, they will not starve to death like animals do when they do not eat. In contrast, if carnivorous plants are not given sufficient light, their energy source will be completely cut off, and they will actually "starve to death".

So, if you want to grow a carnivorous plant, don't be too concerned about feeding. Light is more important than feeding.

Are carnivorous plants picky eaters? Let’s answer this question dialectically—they are both picky and not picky.

They are picky eaters because of the size of the food. For example, if a small Venus flytrap is too big for it to catch, it will easily escape and naturally fail to eat it. If you force feed it too large food, such as a piece of shrimp, the leaves will rot.

Insects are also the best types of food. Pork, fish, eggs, etc. are not suitable for feeding them because these foods are usually hard in texture and may contain high salt.

It doesn't matter whether the insects they feed are dead or alive, because carnivorous plants do not rely solely on the struggle of their prey to feel stimulation and start digestion. For example, the Venus flytrap requires mechanical stimulation to trigger the clamp to close at the beginning, but as long as the prey is caught, even if it is dead, the proteins and other chemicals on its surface can still stimulate the clamp to further start the digestion process.

They are not picky eaters because some carnivorous plants can indeed "eat" a wide variety of foods. For example, the diet of pitcher traps is relatively wide. For some pitcher plants, anything that falls into the pitcher (such as leaves, animal feces, dust, etc.) and releases nutrients after decay can be absorbed.

Of course, if too much food is fed artificially, it will cause the bottle to rot and stink. When growing carnivorous plants at home, you don't need to feed them anything, just ensure that they have sufficient sunlight and water. It is enough for them to eat small flies, ants, spiders, etc. indoors as long as they can catch them by themselves.

In addition, there are many types of carnivorous plants, which live in different environments and are good at eating all kinds of things. Carnivorous plants such as Drosera chinensis and Drosera scoparia have leaves close to the ground and mainly catch ants and spiders crawling on the ground; Drosera scoparia and Drosera striata have leaves extending into the air and mainly catch flying insects; aquatic carnivorous plants such as Bladderwort and Raccoon grass mainly catch prey in the water and even some impurities and debris; terrestrial Bladderwort and Spinella striata mainly catch very small prey in the soil and even single-cell protozoa.

Among the "masters" of the pitcher plant family, which are not picky eaters, some can even occasionally catch some small vertebrates; some can attract small mammals to defecate in the pitcher; some can also attract some frogs or mosquitoes to lay eggs in the pitcher, help eat the debris that falls into the pitcher, and finally absorb the nutrients in their feces. So, from this perspective, carnivorous plants are indeed not picky eaters.

Knotweed

Blooms Sundew

Can carnivorous plants "eat" their food like animals? No.

First of all, carnivorous plants do not have stomachs and intestines, and cannot eat food into their stomachs like animals do. Some animals also do not eat food into their stomachs, such as starfish, which spit out their stomachs to wrap the food and digest the food outside the body. This is very similar to carnivorous plants, whose insect traps are equivalent to stomachs, digesting and absorbing food directly outside the body.

But don't think that after food is digested and absorbed, it disappears or only a little bit of residue remains. In fact, after food is digested and absorbed, there will still be complete remains, and the size may not even change. This is mainly because insects have exoskeletons, which are not easy to digest and absorb. The digested part is mainly the protein in the insect's body, so the appearance of the insect after digestion is not much different from before.

The digestion and absorption process of carnivorous plants may not be as magical as imagined, but their hunting process is indeed amazing. Among them, the performance of the Venus flytrap is the most attractive.

Each leaf of the Venus flytrap has a shell-shaped clamp on the top, and each clamp has a row of thick teeth on the edge. When the clamp is closed, these teeth will cross together to prevent the prey from escaping. There are 6 tentacles on the inside of each clamp, 3 on each side. When the prey touches a tentacles for the first time, the clamp will not move. When any of the 6 tentacles is touched for the second time, the clamp will close quickly within one second. At this time, the clamp is only loosely closed, and there is still a certain space between the two petals of the clamp, and the prey can even walk back and forth inside. But the chemicals on the surface of the prey will further stimulate the clamp to gradually clamp over a few hours, and secrete liquid to suffocate the prey to death.

In the following weeks, some of the protein in the prey will be broken down into amino acids or simpler nitrogen-containing inorganic substances by the protease secreted by the Venus flytrap and the action of bacteria. These will be dissolved in water together with other inorganic salts and absorbed by the clamps. After that, the liquid will gradually stop secreting, the clamps will reopen, and the intact but flattened remains of the prey will remain on the clamps forever, taking up a certain amount of space. But don't worry that the Venus flytrap will "use up" the clamps - it will keep growing new leaves, and there will always be new clamps to use.

Venus Flytrap

Do all carnivorous plants move? No.

In fact, quite a lot of carnivorous plants are immobile. On this topic, the most misunderstood is the carnivorous plant that uses bottles to catch food.

Bottle hunting is a major hunting method of carnivorous plants. Their hunting tool is a bottle-shaped trap, which usually contains liquid and has a bottle cap at the mouth. The bottle mouth can often secrete droplets, which are generally sweet, and some can also emit a strong smell to attract insects. When insects accidentally fall into the bottle, it is difficult to escape and eventually drown in the bottle. Many people think that when prey falls into the bottle, the bottle cap will be closed to prevent the prey from escaping. In fact, the bottle caps of all carnivorous plants that use bottles to hunt are all immobile.

So how do they prevent their prey from escaping? Generally speaking, the inner wall of a pitcher trap is very smooth, and some even have inverted hairs. In addition, there is liquid in the pitcher, so once the prey falls into it, it is very difficult to climb out. The liquid in some pitcher plants is sticky, which makes it even more difficult to escape. Some pitcher plants have thin and tall pitchers with small internal spaces. Once an insect falls in, it is like falling into a deep and narrow well, with almost no chance of climbing out. The inner wall of the pitcher plant's pitcher also has an inverted edge that folds inward, and the mouth of the pitcher also has a row of barbs that grow inward, which can also prevent prey from climbing out.

The question is, if the bottle cap is not used to cover the bottle to prevent prey from escaping, what is the use of the bottle cap? It is currently believed that the bottle cap may be used more to attract prey - some bottle caps have colorful and transparent patterns, and some bottle caps can secrete sugar to attract prey to come and eat. In addition, the bottle cap can also play the role of shielding rainwater, preventing the bottle from tipping over due to excessive water storage and weight.

Honey juice on the bottle cap of yellow pitcher grass

Can growing carnivorous plants reduce indoor mosquitoes and flies? The answer is yes—basically no.

First of all, carnivorous plants don’t always attract all kinds of indoor insects that you hate. For example, mosquitoes are much more attractive to skin that emits body temperature and sweat than to carnivorous plants. Cockroaches and house ants that like dark and humid indoors, and carnivorous centipedes generally don’t run to carnivorous plants. In addition, attracting insects is not necessarily a good thing - there are more indoor ants in the south, and if you plant a pitcher plant, the nectar it secretes may attract more ants into the house, which is a disaster for people with trypophobia.

Secondly, the hunting efficiency of carnivorous plants is not that high, and they often catch prey by chance. Flies that accidentally fly into your home may be caught by Venus flytraps or stuck by sundews. But more often than not, they can’t catch them. For carnivorous plants, preying on insects is not a matter of life and death, so they don’t try every possible means to catch prey like carnivores do. Instead, they are more Buddhist, and they “eat” if they can catch them, and it doesn’t matter if they can’t catch them, because they won’t starve to death anyway.

So, if you want to grow carnivorous plants, it’s best not to expect them to help you implement the concept of “biological control” in the fight against mosquitoes.

Author: Zeng Gang (Xishuangbanna Tropical Botanical Garden, Chinese Academy of Sciences)

Source: Science Institute

Published: 2021-04-27