April 22, 2024


in the movie of the shop of horrors (1986) a most peculiar plant appeared. Her name, Audrey II, already denoted that she was special: to grow she needed to be nourished by human blood. A plant that eats animals, what a fantasy! But, yes, it would be necessary to take into account hundreds of species that do the same. Although they do not need our meat, like Audrey II, they are waiting for insects and other small animals to fall into their traps to feed themselves.

The gift that plants have to grow in almost any imaginable growing situation has led them to generate strategies that are the most absurd, in the eyes of mammals. In the case of carnivorous plants, they have adapted to vegetate in environments with high rainfall or linked to watercourses, where the nutritive salts of the substrate are dissolved. Thus, they have to thrive in less fertile places. For this reason, they use traps to hunt bugs and microorganisms that complete their daily diet. From them they will extract the nitrogen or phosphorus necessary to form leaves and complete their reproductive cycles, which are very demanding of energy.

It is thought that there are certain plants, also common in fields and cities in Spain, which are precursors in this matter of consuming animals. Two of these are the ubiquitous shepherd’s purse (Capsella bursa-pastoris) and the teasel (Dipsacus fullonum), also called carding thistle because of its use for this textile function. In the case of the shepherd’s purse, which we can find on any sidewalk in our towns and cities, it is its seed that releases a sticky mucilage that attracts microorganisms such as nematodes. When they get trapped in that liquid, they die, and it will be the new seedling that emerges from the seed that takes advantage of the nutrients that the captured unwary possessed and that have been decomposed by natural processes.

The aforementioned thistle is also capable of drowning small insects, this time in its own leaves. These, which grow opposite each other and sitting on the stem, form a small tub at the base. When it rains, it is filled with water, and a multitude of flies and beetles will drown there. Again, it is thought that the decomposition of the soft parts of its tissues makes the plant capable of absorbing the nutrients that are generated. For all these reasons, both species are considered protocarnivorous plants, skilled at catching their prey in some way, but without the ability to directly absorb their nutrients. The matchmaker (plumbago auriculata), the popular climbing plant with sky blue flowers, would be another of these protocarnivores, with its sticky glands that accompany the inflorescences.

A shepherd's purse plant showing its seed-filled fruits in a Madrid tree pit.
A shepherd’s purse plant showing its seed-filled fruits in a Madrid tree pit.Edward Beard

But there are plants with even more sophisticated and obvious strategies in the game of coaxing and gulping down the prey, with really ingenious attractive traps. The most striking is a species well known to the public fond of nurseries and florists: Dionaea muscipula. Called the Venus flytrap, this plant looks more Venusian than Earthling, because it’s as if it landed from another planet. With its seemingly dangerous jaws, our fingers have nothing to fear. They should worry flies and worms, for whom their transformed leaves are a deadly prison once they close in on them.

Miguel Azañón, founder and CEO of the Plantas Carnívoras España nursery, markets this exciting species. It is his star product, and it also brings together collector’s varieties produced in the laboratory. “We have cultivars that are in high demand, such as ‘B52’ or ‘Akai Ryu’, the latter red in colour”, says Azañón, “and some that are very popular, such as ‘Microdent’, with many very fine teeth, or ‘Fuzzy Tooth’, with fused teeth, which is very funny”, he concludes. Both one and the other will close when any insect walks inside the mouths of the plant, and touch two of the inner cilia, which are the triggers for the closing response of the trap. In this way, they avoid closing themselves off from other stimuli that would not generate a reward but rather an energy expenditure due to the movement.

Contrary to what many people think, Venus flytraps are very easy to grow. Azañón sums it up like this: “They need the sun outside, and they are not afraid of the cold. They are not tropical plants ”, he emphasizes, but in their place of origin they have winters where temperatures drop a lot. That place is North and South Carolina, in the United States, so its distribution is also peculiar and circumscribed to a relatively small area.

Perhaps irrigation is another of the points of failure in the cultivation of this plant. “That is the main thing: the water”, points out Azañón, “which must be soft and without mineral salts. One of the mistakes is to use tap water in regions where there is hard water, rich in calcium and magnesium, since it accumulates in the substrate and ends up killing the plant”. For this reason, in these places the expert recommends using rainwater, air conditioning, bottled mineral waters with weak mineralization… “Anything with a low salt content,” he emphasizes. In regions with soft water, such as Madrid, it can be used without risk of damaging it. For the Venus to be comfortable, it is convenient that the substrate is always humid, “with the exception of the cold months, which is when it benefits her that the substrate dries slightly”, adds Azañón, since it is in a rest period and it is not so demanding in risks. At that time it is possible to lose a large number of leaves, but do not worry: it will regrow when the temperatures rise.

Dionaea seedlings showing their traps.
Dionaea seedlings showing their traps.

Once the challenge of water has been overcome, it must be clear that it is not convenient to put it in an aquarium, or add fertilizer, or pieces of meat, something that the naturalist Charles Darwin did in his exhaustive experiments with these plants, of which he published a book that continues to be a reference for these voracious species. Miguel Azañón completes the Venus flytrap care decalogue with these simple tips: “It is not necessary to transplant them, beyond perhaps making some division to separate one of the daughters that the rhizome of the mother plant develops at the beginning of spring. If it is done”, he adds, “it is transferred to a slightly larger pot, preferably plastic, with blond peat and without any fertilization”.

It is quite possible that, if the plant is happy, it will bloom. In this case, it is better to cut the inflorescences that come out, since the plant spends a lot of resources in forming them, as well as for the small blackberry that is its fruit. If we have seen this process before, and we want a stronger plant, they are cut as soon as the floral rod appears. Be careful not to get your fingers too close to their traps when we do it, lest we take a bite.

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