Sunday, 19 May 2013

Carnivorous Plants FAQ - Frequently Asked Questions

What is a carnivorous plant?

A carnivorous plant is a type of plant which lives in areas where the soil is poor in nutrients and has evolved to get its nutrients by attracting, trapping and digesting insects (and in some cases, small rodents).

How many species of carnivorous plants are there?

There are nearly 700 species and sub species of carnivorous plants known to exist.

How do they trap their prey?

The three ‘main’ ways that these plants trap their prey are ‘pitfall’ traps, ‘flypaper’ traps and ‘snap’ traps.

Pitfall traps are typically long and narrow. Insects walk around the slippery ‘lip’ of the plant. If they fall in, it is hard for them to get out as there are downward pointing hairs and all sides of the interior of the plant are slippery. The North American pitcher plant (Sarracenia) get narrower the further down to the bottom it gets. This means that if, for example, a fly gets trapped, it isn’t able to extend its wings to get out. Also, the vibration of it attempting to use its wings can often lead to it falling further down the trap. Tropical pitcher plants (Nepenthes) slightly differ to this as there is often water/digestive enzymes at the bottom of the trap which causes the prey to drown.

Flypaper traps, such as Sundew, contain sticky tentacles. Insects are attracted to these tentacles and when they land, the get stuck. Over time, these tentacles wrap themselves around the insect to prevent it from escaping and bring it closer towards the centre of the leaf. Depending on what type of sundew it is, the leaves themselves can wrap around the insect. Once the insect is in place, the plant releases its digestive enzymes to consume the nutrients from the insect.

Snap traps are the type of traps that a venus flytrap has. Insects are attracted to the traps because of the colour and sweet nectar. Each trap has 6 trigger hairs, 3 on each side. When one of the hairs is touched, it starts a 30 second countdown timer. If the same hair or another hair is touched within that time, the trap will shut. It is still under debate as to exactly how the trap shuts. The long hairs at the top of the flytrap are to help prevent insects from escaping, but they don’t completely shut immediately. When the trap closes, they come close together enough to trap large flies but still leave space incase it has trapped prey so small that they aren’t worth the plants energy for the digestive process and can let the insect escape.

How big do they get?

Venus flytraps (the plants themselves) usually grow to be about 15 cm across. The traps themselves don’t typically get any bigger than 5cm across.

Pitcher plants vary a great deal, but the North American pitcher plant can grow up to 3ft tall (after several years of good conditions, though they are typically smaller. My tallest one is about 2ft). Tropical pitcher plants are usually up to 20 cm in length (though typically smaller). Some of the largest ones in the world are wide enough to put your fist in!

Sundews vary drastically on size, depending on the species. The smallest ones are no more than 1cm across. The largest ones can be just over 1ft in length.

Are they easy to grow?

The most common question I get asked. The answer is yes, I think they are. Obviously with any plant, there are ‘ideal’ conditions to get the most out of them by keeping them in x amount of humidity or x amount of sunlight. Truth is, certainly for the venus flytrap, I’ve kept them room, the kitchen windowsill, outside, in a mini plastic greenhouse and in a full sized greenhouse and obviously conditions vary.

The most important rules of thumb for the plants that I know most about (Venus flytrap, Pitcher Plant and Sundew) are:

1.      ONLY give them rain water. Tap water contains chemicals that can harm the plant.
2.      Keep them standing in about 2-3 cm of rainwater
3.      Keep them in a sunny position if possible. South facing windowsill is ideal but as long as they get some sunlight, it should be ok.
4.      Prune off dead bits

Ahh but food. What about feeding them?

If they are outdoors (I’d recommend bringing them in during winter if you keep them outdoors) they should get enough food by themselves. If they are indoors, it might be good to feed them a fly or two maybe every few weeks. If you feed them insects, they should be alive for the VFT and sundew as they respond to the movement of their prey, whereas pitcher plants will eat whatever you put in them, alive or dead.

Will these plants hurt me? After all, they are carnivorous

Yes they will eat you, probably when you are sleeping. Only joking of course. It is kind of odd them being called carnivorous plants, since insects aren’t meat. But no, these plants will not harm you at all. If you check my youtube channel ( you will see I have several videos of me putting my fingers inside the traps. There is no pain, its only two leaves closing on your fingers.  I wouldn’t recommend putting your finger in the traps of the flytrap only because it harms the plant as it uses up energy to close itself. As for the pitcher plants and sundews; the pitchers have no moving parts and the worst thing you’ll get from sundews is sticky fingers.

Do these plants make for good fly repellents?

Yes and no. A repellent is something that drives insects away. These plants will attract them. However, if you have an area where insects (such as flies) frequently visit, then these plants will divert there attention and may even catch a few! Also – worth noting that pitcher plants (Sarracenia) are better at attracting insects and can catch more than the VFT’s

What soil should they be repotted into?

If you repot one of these plants, its usually best to either buy the correct compost from one of the carnivorous plant retail websites, or buy 'nutrient-free' peat from your local garden centre. Make sure the peat is without any nutrients or the plant will not survive.

So what do you think the best plant is?

The venus flytrap will always be my favourite plant. The way it looks, the mechanism of its traps etc. But the truth is, it’s a bit of a false hero. It’s the most well known carnivorous plant of them all, by far, but its not the best. The best plant for attracting insects than can catch the most are the pitcher plants.
When I go into the greenhouse in the middle of summer, there are maybe one or two flies walking around ALL of my flytraps, whereas some of my pitcher plants have that amount of flies walking around a single trap. Most of the flies hang about around the pitcher plant area and only occasionally visit the venus flytraps.

There’s also the quantity of insects that can be trapped. A VFT might have 4 or 5 traps, but will typically trap one insect at once, and that trap can be closed for over a week while the digestive process is taking place. Whereas if a pitcher plant has that many traps, and its of decent size (say 1ft), insects will keep falling into it and it can catch several dozen insects per trap. I have known pitcher plants to catch so many flies that they get filled to the rim (literally) and if an insect falls into the trap, it will walk over the other flies and climb out again.

That being said, when an insect lands on a pitcher plant, more often than not, it won’t get trapped. Whereas if an insect of decent size (i.e.: small) lands on a sundew, its instantly stuck. Same as if a fly walks across the trap of a flytrap, chances are it will get trapped. In other words, Pitcher plants are the best at attracting and can catch by far the largest numbers of insects, but sundews and venus flytraps are better at catching the insects once they land.