Sensing the Prey
The leaves of the Venus Flytrap are divided into two parts, called lobes, and the surface of these leaves is covered with stiff, short hairs called "sensitive hairs." When a fly, small moth, spider or other tiny animal touches two of these hairs in succession, the plant reacts by closing the lobes. If a raindrop, for instance, touches just one hair, nothing happens--the flytrap conserves its energy and waits for the proper signal.
Insects are rich in nutrients, particularly nitrogen, that are lacking in the spaghnum bogs of North and South Carolina, where the Venus Flytrap is native. Its primary source of energy, however, is photosynthesis, the same process that other plants use to build carbohydrates and other organic compounds from sunlight and carbon dioxide.
Closing the Trap
When triggered, the lobes come together quickly, often within one second, but do not close completely for a few minutes, possibly to give the smallest insects space to escape between the finger-like extensions along the edge of the leaf. They would be too small to be worth the energy of digestion.
The struggles of a trapped insect cause the lobes to come together tightly, sealing it inside. If a tiny stone or piece of leaf has been trapped, the leaf will open about 12 hours later. A single leaf is limited to seven closures during its lifetime.
Once the animal is caught, glands on the surface of the leaf secrete digestive enzymes that dissolve the soft, nutrient-rich parts of the prey, plus an antiseptic liquid that keeps the insect from rotting before it can be digested.
The digestive fluids are then reabsorbed by the leaf and, 5 to 12 days later, it opens again, releasing the hard exoskeleton of the insect as waste.