Bug-Eating Snapping Plants

Most of us have heard of the Venus flytrap. We know it is a plant that eats bugs, and we may even know that it catches live bugs in a trap. What we may not know is why it does this, how fast it is, and how the snapping motion works. This is a plant that does not have goo that the bug gets stuck in, but rather it is a plant that clamps two sides of a trap together in 100 milliseconds (something close to a tenth of a second) trapping even the fastest fly. If you have ever tried to grab a fly with your bare hands, you know how tough that is to do, and the flytrap does not have muscles to do it with.

The catching mechanism of the Venus flytrap is actually a modified leaf. Each side of the trap is fringed with trigger hairs and bisected by a deep fold. Each half of the leaf is flexed in a way that it bends away from the juncture point of the leaf. That means that as a bug lands on the leaf it appears that there is nothing around him. When a trigger hair on the edge of the leaf is disturbed, the leaf begins to slowly close. There is a threshold when the leaf reaches a certain amount of curvature, it will pop back into its original shape. A good illustration is a toilet plunger. If you push down on a plunger a short distance, it will pop back into its original shape. If you keep pushing however, you can eventually reach a point where the plunger will pop into a new configuration where the curvature is reversed from its original position. The only way you can get the plunger back to its correct shape is to force it back. There is a point when you put enough force on it to force it back, it will pop back to its original shape. Because the plunger can exist in a stable way in both positions, it is said to be bistable. That is also what happens with the Venus flytrap.

When the Venus flytrap sets its trap, it opens its two halves and flexes them back to one stable position. When an insect disturbs one of the leaf hairs, the plant moves the leaf a few hundredths of an inch so that it is right at the trigger point. The instant that trigger point is reached the leaf pops to its second stable position and the hairs make it so that even if the insect starts to fly it will get caught. The plant then slowly continues to close the two sections so that they are airtight and the plant secretes enzymes that dissolve the insect.

Plants like the Venus flytrap live in bogs that are more acidic than normal and have very few nutrients. The insects provide the missing nutrients and allow the plants to live in an area that would otherwise be void of life. Bladderworts, pitcher plants and sundews all eat bugs allowing life in these biological wastelands, but they have specially designed structures that allow this to happen. The Venus flytrap is uniquely designed to trap insects in a special way--one that involves so many working parts it is difficult to conceive of how it could have come into existence by chance. God has designed complex systems to serve every kind of ecological condition so life exists even in environments that you would never expect life to survive. The acidic bogs are just one of these.

--Reference: Natural History, June 2005 pages 26-27.

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