The peppered moth, Biston betularia, is a textbook example of natural selection, demonstrating rapid evolutionary change. Its survival strategy, particularly its camouflage, is profoundly linked to its environment. The moth’s distribution and habitat requirements provide the physical foundation for one of the clearest observations of evolution ever recorded.
Global Geographic Range
The peppered moth is a temperate species with a vast distribution across the Northern Hemisphere. It is found throughout Eurasia and North America, inhabiting a broad range of longitudes and latitudes. The species is widespread across Europe, and its range extends across Russia, Mongolia, and China in Asia, including the Himalayas.
In North America, the peppered moth is found coast-to-coast, from the eastern United States to the Pacific Northwest. This extensive global coverage indicates the species’ adaptability to different temperate climates. While its geographic range is broad, the most well-known evolutionary shift occurred in specific, localized, industrialized regions, primarily in Great Britain and parts of Europe and North America.
Specific Habitat and Micro-Environment
The specific habitat of the peppered moth centers on areas rich in trees, which includes deciduous and mixed woodlands, parks, hedgerows, and even urban gardens. The moth’s life cycle is intrinsically connected to the vegetation in these environments, particularly for its larval stage. Caterpillars are polyphagous, feeding on a wide variety of trees and shrubs, such as birch, willow, oak, hawthorn, and poplar.
Adult moths are nocturnal, but they spend the daylight hours resting on the trunks and branches of trees. They rely on camouflage in this resting position to avoid avian predators. In unpolluted areas, the light-colored, speckled form (typica) blends seamlessly with tree bark covered in pale lichens.
The Evolutionary Significance of Their Location
The location where the peppered moth rests—the tree surface—became the site of intense selective pressure due to industrial melanism. Before the Industrial Revolution, the light-colored moth was dominant because its pattern was camouflaged against lichen-covered trees. The few dark-colored moths (carbonaria), a naturally occurring genetic mutation, were easily spotted by birds and had a low survival rate. During the height of industrial pollution, coal-burning factories released vast amounts of soot that killed the lichens and blackened the tree trunks. This change reversed the selective advantage, making the light form highly conspicuous to avian predators. The dark form was now better camouflaged against the sooty bark and survived to reproduce more successfully, providing an observable demonstration of natural selection.