Peppered moth is an inconspicuous (not showy) moth found throughout the Northern Hemisphere that has become famous as an example of natural selection. Natural selection is the process by which individuals better suited to their environment tend to survive and leave more descendants. It is an important principle in the study of evolution, the process by which living things develop over many generations. The peppered moth is also known in North America as the pepper-and-salt geometer. The moth has a wingspread of 1 1/2 to 2 1/3 inches (4 to 6 centimeters). Its wings are usually white with thin black lines and dark specks, giving it a “peppered” appearance.
The peppered moth’s usual light-colored wing patterns provide protective coloration. These patterns help camouflage the insect when it rests on the trunks or branches of light-colored trees covered in lichen, making the moth harder for birds to spot and eat. A small percentage of peppered moths, however, have dark wings. These moths are generally much easier for birds to see against light, lichen-covered trees. During the Industrial Revolution, air pollution killed much lichen and darkened trees with soot. The Industrial Revolution was a period of rapid industrialization that began in the 1700’s. The lighter moths stood out against the darkened trees and were easy prey for birds. Individuals with dark wings were in turn camouflaged, giving them a better chance to survive and reproduce. Over 50 years, the population changed from mostly light-colored individuals to mostly dark individuals, an example of natural selection in action.
Later, countries in the Northern Hemisphere reduced their output of industrial pollution. Tree bark in those areas returned to its natural color, and lichens grew back. Over time, populations of peppered moths have returned to favoring the lighter varieties, another example of natural selection.
