Maybe we don't give caterpillars enough credit...
The Ostrinia nubilalis and Ostrinia scapulalis are two very closely related species of pest caterpillars that only differ in their host plant. While Ostrinia nubilalis, which is commonly called the corn borer, "spends spring and summer feeding on its corn stalk before spinning a cocoon for the cold winter," the Ostrinia scapulalis has the same life cycle except it feeds on a weed known as mugwort. Up until recently these two caterpillars were classified as the same species, because the particular host plant seemed unimportant to scientists. After closer observation, however, scientists realized that the cultivation of corn has created a distinct difference between these two species. While mugwort is never harvested or grazed, corn stalks are cut down leaving only about 6 inches of the stalk in the ground. The harvested stalks are then burned or fed to livestock once the corn has been removed, either of which leads to the certain death of any caterpillar cocoons attached to the harvested stalk. The corn borer, however, has adapted in order to survive the harvest by climbing down the stalk before it spins its cocoon.
This example of evolution was very successful and occured fairly quickly relative to the evolutionary time scale, because of the fast turnover of generations (one each year) and the lack of contamination of the sample. There was no worry of a caterpillar who did not move down the stalk before spinning its cocoon of passing on its genes, because it would die before it got the chance. I also found this example interesting, because nature has almost given us a control with the Ostrinia scapulalis, which have not developed the same "descending behavior, called geotaxis," because it has no evolutionary advantage since mugwort is not cut down. This clearly shows evolution at work.
Darwin certainly wouldn't have taken these caterpillars for granted.
Full Article: http://www.nytimes.com/2010/04/27/science/27obborer.html