If you've been patiently waiting for your Venus flytrap (Dionaea muscipula) to open, and it still hasn't happened, your only option is to wait longer. In order to exclude bacteria and fully enclose its digestive enzymes, the traps on these carnivorous plants remain firmly closed during the five to 12 days it takes to eat a meal. The trap will open sooner, in a mere 24 to 48 hours, if it was a raindrop, twig, or curious human that triggered its closure. This reopening, however, occurs only once the plant determines that it has failed to trap a food source. A closed trap won't open until the plant decides it's time. In some cases, individual traps won't reopen at all but will instead die and fall off the plant. This occurs at the end of each trap's useful life. You can manually pull a trap open, but doing so could harm the plant, and it will simply close the trap again in a few hours if it's able.
The Trap is Sprung
Venus flytrap leaves grow in tandem, forming pairs. These leaf pairs, known as traps, sit opposite each other and work together to catch and hold flies and other insects. Each trap contains several tiny trigger hairs. When a foreign object disturbs these hairs, the trap snaps shut, hopefully imprisoning a tasty insect. The plant remains open, however, until the trigger hairs experience at least two disturbances in rapid succession. This helps prevent the plant from closing unnecessarily if an insect lands in the trap and then quickly flies away.
The trap is now sprung, but it closes only loosely at first. If an insect truly is stuck, it will struggle to free itself. As it does, it continues to rub against the plant's trigger hairs. When the struggling insect stimulates the trigger hairs repeatedly, the Venus flytrap knows for sure that it has caught a meal. It's only then that the trap closes more tightly and begins to secrete the digestive juices necessary to kill bacteria, destroy fungi and break the insect down into nutrients. This process takes five to 12 days, depending upon the size of the meal. After digesting the insect, the trap opens again to essentially spit out the dead bug's remaining exoskeleton and catch its next victim.
Once in a while, the trigger hairs inside a plant's trap react to a stimulus other than food. It's possible for a raindrop, falling leaf or another small object to trigger the trap. Venus flytraps have an interesting way of responding to this possibility. The trap closes when a stimulus touches its trigger hairs, but only loosely. It then waits to see whether a struggling insect continues to stimulate the trigger hairs. If nothing happens, the plant will reopen the trap in a day or two. This ingenious system allows the plant to conserve energy. Rather than clamping down on itself and beginning the digestive process unnecessarily, it instead waits to see if it has actually caught a meal. If it hasn't, the plant simply resets the trap and waits for its next stimulus.
This built-in false alarm system is sometimes a source of frustration for Venus flytrap owners. It takes live prey to stimulate a flytrap's digestive process, so tossing a dead fly into one of the plant's traps may cause it to close, but the trap will soon open again rather than digesting the meal as desired. Feeding live prey is best, but if you do offer your plant a dead insect, you'll need to stimulate the trigger hairs repeatedly as a live insect would. To do so, first place the insect into one of the traps. If the trap doesn't close, use a pencil point or toothpick to stimulate the trigger hairs until it does. Don't use your finger, as the oil from your skin is bad for the plant. Once the trap has closed, gently grasp the trap between your thumb and index finger, and gently rub it until it closes more tightly, signaling the beginning of digestion.
The Last Supper
The leaves on a plant don't live forever, and the same is true of the Venus flytrap. Each trap, or leaf pair, on a flytrap has a limited lifespan. After closing three to five times, the traps on the plant will remain closed, turn black and die. Hopefully, each closing will imprison an insect and feed the plant. The trap will die after closing a certain number of times, however, even if each closing was a false alarm that failed to result in a meal. New traps replace the dying ones as the plant continues to grow.