Pitcher Plants

Carnivorous pitcher plants eat insects. There are many species of pitcher plants that grow in various parts of the world. They often grow in areas where the soil is nutrient-poor, so the plants get their energy from bugs while keeping the ant and insect population under control.

Pitcher plants capture the insects by causing them to slide into their “pitcher” which is a modified leaf. Sweet nectar attracts ants or other insects to the slippery edge of the pitcher. The insect falls into the pitcher, and the slippery sides prevent it from escaping. After drowning in liquid at the bottom of the pitcher, the insect is digested by enzymes, and the plant absorbs the nutrients.

The Nepenthes rafflesiana is a tropical pitcher plant that grows in Asia. Scientists noticed that there were rarely any insects in the trap. The impression of the biologists was that the traps were poorly designed and not very efficient. Ants were crawling around on the nectar-rich collar of the pitchers, but not falling in. Then the biologists noticed that when it rained, ants were falling into the pitcher in record numbers. They tested their observation by wetting the pitcher plants, and they discovered that large numbers of ants were captured.

The traps that the biologists believed were inefficient turned out to be very well designed. The way it worked was that ant scouts would come out to the plants and find the good tasting nectar. The scouts would return to their colonies and bring many more ants back with them. Then with many ants on the edge of the pitcher, a little rain can bring a good meal into the plant. “Slippery when wet” is the key to an efficient trap.

So the ants get nutrition from the pitcher plant when it is dry. Add a little rain, and the pitcher plant gets a banquet. Not all of the pitcher plant species work only when wet. However, there are pitcher plants in North America and Australia which work the same way. Since these plants in diverse parts of the world have come up with the same clever idea, scientists have a name for the phenomenon. They call it “convergent evolution” in which different species and sometimes totally unrelated species have independently “evolved” the same characteristics or methods. We call it common design by a common Designer.
© Roland Earnst

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