A garden with different habits
Some leaves snap shut on insects. Others stick them down, let them fall or suck them out of the water. Enter a world where the plant is the predator.
The trap is a leaf. The three small hairs inside each half detect touch.
Noah Elhardt · Photograph · CC BY-SA 2.5
Luc Viatour / Lucnix.be · Photograph · CC BY-SA 3.0
Start with a touch
An insect bends a trigger hair. An electrical signal follows. If another arrives soon enough, the two halves of the leaf snap shut.
Touch twice, less than 20 seconds apart.
The trap is waiting.
Simplified model: each touch here creates one signal, retained for 20 seconds. In the real plant, the response depends on movement and conditions; a single bend of a hair can produce two signals. Burri et al., 2020 ↗
Closing is just the beginning. The movements of trapped prey can generate further signals that help trigger digestion.
For nutrients that are hard to find in the soil. Many carnivorous plants grow in places short of nitrogen and phosphorus. Prey supplies some of these elements; sunlight still provides energy through photosynthesis.
The traps are modified leaves. Flowers retain their role in reproduction. Pavlovič et al., 2014 ↗
Five ways to catch prey
Choose a plant. Look at its leaf and follow what happens to an animal that arrives there.
Dionaea muscipula
Trigger hairs detect movement. Electrical signals set off the rapid closure of the two halves of the trap.
Look closely
The trigger hairs are inside. The long spikes around the edges form the bars of the trap.
Drosera capensis
An insect gets stuck in the secretion on the leaf. Glandular tentacles, and in some species the leaf itself, can bend towards the prey.
Look closely
Each drop sits at the tip of a tentacle. The dew-like appearance conceals a sticky surface.
Nepenthes villosa
Prey falls into the liquid inside the pitcher. In many Nepenthes species, the wet rim is extremely slippery for insects.
Look closely
A ribbed rim surrounds the opening. The lid above it does not close over the prey.
Utricularia vulgaris
The plant pumps water out of the trap. When the door gives way, the pressure difference drives water and prey inside.
Look closely
The little swellings on the submerged branches are traps. The flowers can rise above the water.
Genlisea violacea
Underground leaves branch into twisted tubes. Hairs inside make it harder for tiny organisms to turn back towards the exit.
Look closely
The white structures are leaves modified into traps, lifted out of the growing medium so they can be seen.
Underwater, everything changes
Researchers filmed Utricularia traps sucking water in within less than a millisecond. Opening and closing the door add time to the full sequence, which is still difficult to follow with the naked eye.
< 1 ms · suction, in the 2011 study
Water has been pumped out.
Slowed explanatory sequence; shape and movement are schematic. The submillisecond duration describes suction, not the entire sequence. The study included U. vulgaris, the photographed species. Vincent et al., 2011 ↗
Now recognise the trap
Three situations. Choose the mechanism that explains each capture.
Sundew. The drops on its tentacles are a sticky secretion.
Bladderwort. A pressure difference creates a current that carries prey into the trap.
Pitcher plant. The pitcher retains its prey; the lid does not work like a jaw.
The round-leaved sundew, Drosera rotundifolia, is native to Romania too. The gallery photograph shows another species in the same genus, Drosera capensis.
Kew · Plants of the World Online ↗Trap research, botanical explanations and photographs that let you see for yourself.
Image resized; some views show a partial crop.
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