The principle of snap traps is used only by two monotypic genera, namely by the Venus Flytrap (Dionaea muscipula) and by the aquatic Water Wheel Plant (Aldrovanda vesiculosa). With a duration of circa 0,1 seconds the closure of a snap trap belongs to the fastest movements within plant kingdom. Albeit this genius snap traps are not a modern invention of evolution. In the Czech Republic fossil finds of a antecedent of the modern Water Wheel Plant, the 65 millions years old Palaeoaldrovanda splendens, were made.
Let explain me the trap mechanism by taking the example of the Venus Flytrap. The mechanism of the Water Wheel Plant operates almost identical. The leaf of a Venus Flytrap consists of two components. It consists on the one hand of a broadened leaf stalk and on the other hand of the basic leaf blade, which represents the trap and consists of two interconnected halves. Each half of the leaf blade shows two different bristle types. The rigid margin bristles and mostly three on the leaf blade located feeling bristles. By use of nectar production and an intensive-red colouring as well as an UV-signature insects are attracted, which sit down on the leaf blade. The feeling bristles are through a joint on the leaf blade fixed, hereby the feeling bristles can fold away. A movement of the feeling bristle is registered by use of a sensor. If the insect touches a feeling bristle or two different within of 20 seconds twice, then in the leaf blade occurs a tiny electrical signal, which spreads out with 10 cm/second within the leaf blade and leads to a closure of the trap. Fundamentally, the closure is a passive mechanism. Energy is released, which the plant has previously invested in the spreading of the trap. Thereby the situation is analogous to the bladder traps of the blatterwort. Both leaf blades are slight concave (inward vaulted), what is achieved by a 10-per cent contraction of the outside compared with the inside. The exact biochemical and physiological mechanisms, which cause a turn of the concave into a convex leaf blade, are still not exactly explained despite intensive research.
After triggering of the trap, in the first instance, the plant is in an intensive test mode, before it proceeds with the utilisation phase. At first the plant checks two things. Firstly: Was just captured anyway an insect or is it just a nuisance alarm. For example only a falling down leaf could have triggered the trap or the insect could escape at the closure of the trap yet again. The quality of the prey is proved on the basis of chemical and tactile sensors. Only if the insect repeatedly touches the feeling bristles in the next minutes, the trap enters the second phase. Secondly: It takes place a weighing up the choices between costs and benefits. The digestive process spens energy, in addition the trap is occupied for some days. The effort is only worthwhile, if the insect has a certain minimum size. Now the initially mentioned margin bristles come into play once more. At first the trap closure is only so far as the margin bristles interdigitate, though the leaf blades don’t touch. A little ant can still escape, a big fly on the contrary not.
At entering the utilisation phase is a circa 10-per cent growth of the trap to observe, by what both leaf blades are rigidly pressed together and the trap is liquid-tight closed. Afterwards digestive enzymes are secreted, the insect is utilised and the trap is reopened after circa one week. The remaining chitinous exoskeleton is removed by rainfalls or by the wind off the trap and the trap is prepared for its next usage.