|Super-specialization among insects is more common than great flexibility. In some cases, however, a specific adaptation that once benefited an insect can suddenly become a liability. Especially when humans are involved. The nocturnal birch moth, or common peppered moth (Biston betularia), normally has pale, speckled wings. It rests during the day on shaded branches and trunks of birch trees. Around Manchester, England, during the industrial revolution, the normally light-colored birch bark was blackened with soot from factories. Birds could now easily pick out the light-colored birch moths, which had once been well camouflaged. Very soon, a formerly rare, dark-colored variety of the same moth began to take over from the much more common light-winged individuals. Until the industrial revolution, the unusual, dark moths had always been at a disadvantage because of their visibility to predators. Now the conditions were reversed, and the light-colored moths became very rare.|
|Sudden changes in conditions, similar to what happened in the event described above, are extremely rare. But when they do occur, they are almost always associated with human actions. Biologists have given the term "industrial melanism" to this kind of sudden, necessary evolutionary change. Today, in some industrialized areas of the United States, almost 90% of the butterflies are melanic, and the landscape is less colorful because of it.|
Left: butterflies drink nectar from flowers and aid in pollination. Below: a bug turns its back on the camera. Photos by Maya Walters.
[arboreal adaptations] [birds] [pollution]
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