Appliance of Science: 'Do Venus flytraps eat flies or melt them?'

I LOVE the way children see things from a completely different perspective. Take this question sent in by six year old Ted….

“Do Venus flytraps eat flies or melt them?”

I’ve known about these carnivorous plants since my own childhood, but I never thought about how they work in quite such an interesting way. So, to answer Ted’s question… they do a bit of both; they eat the flies by melting them. Flies are less of a food for them though, and more of a food supplement.

Like other plants, Venus flytraps (Dionaea muscipula), produce their food by a process called photosynthesis. However, they tend to live on poor boggy soil, where there is not a lot of certain nutrients, such as nitrogen and phosphates. They supplement these nutrients from the insects they eat.

THE TRAPPING BIT

Insets are attracted by the sweet nectar that the plant produces and secretes onto the leaves of the traps. Once something lands on the trap the plant needs to be sure that it is a living thing, not just a piece of dust or debris. This is the really clever part; the inside of the traps have short, spiny hairs, called trigger hairs that can detect movement. If these hairs detect two movements within 20 seconds they trigger the trap to shut rapidly.

The trap does not close completely; it remains slightly ajar for the first few seconds, creating a cage like trap with the interlocking bristles on the edges of the trap leaves. This traps larger insects while allowing very small ones to escape, preventing the plant from wasting any further effort on digesting an insect that is just too small to be of nutritional value.

After a few seconds the trap closes fully, creating an airtight seal. This is important as it prevents any digestive enzymes from escaping and also stops bacteria or fungi from entering and rotting the trap. If an insect is too large for the trap to close fully, then both the insect and the trap may rot and the trap will fall off.

If the trap does accidently close over a piece of debris it will open again within a day or so.

THE MELTING BIT

Once the trap is closed and airtight, the plant secretes digestive enzymes into the space. These dissolve (or melt) the soft, inner parts of the insect; the parts that contain the nutrients that the plant needs. The tough outer skeleton of the insect is harder to dissolve and does not have any nutritional value for the plant.

The whole process takes about five to 12 days. The nutrients are absorbed into the plant and the trap eventually reopens, dropping the leftover parts of the insect to the ground.

DOES IT ONLY EAT INSECTS?

The Venus flytrap is a carnivorous plant, not just an insectivorous one. That means that, as well as insects, it also sometimes eats spiders.

NATIVE CARNIVOROUS PLANTS

The Venus flytrap is not native to Ireland, but we do have many native carnivorous plants, mostly growing in boggy areas. Examples include sundew, butterwort and bladderwort. Each has its own system of trapping their prey, but, just like the Venus flytrap, they then secrete digestive enzymes, dissolving their insides and absorbing the nutrients.

Naomi is a science communicator and mother to three inquisitive children. She can be found at sciencewows.ie

Feel free to email your questions to drhowsciencewows@gmail.com



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