Peppered moth

The peppered moth, known scientifically as Biston betularia, is a nocturnal insect from the family Geometridae. These moths are found across many temperate regions in the northern hemisphere. They live in diverse locations, including North America, Europe, and much of Asia. This includes countries like China, Russia, Japan, and South Korea. The peppered moth is a famous subject in biology. It serves as a primary example of population genetics and natural selection. Scientists use this species to study how groups of living things change over time.

The life cycle of the peppered moth consists of four distinct stages. It begins as an ova, which is a small egg. The next stage is the larval instar, commonly called a caterpillar. These caterpillars are masters of mimicry. They can match the form and color of a twig to stay hidden. Recent research shows caterpillars can actually sense a twig's color through their skin. This allows them to adjust their body color to match their background. This ability helps them avoid being eaten by predators. After the larval stage, the insect becomes a pupa. The pupae stay in the soil to survive the winter. Finally, the adult moth, or imagine, emerges from the pupa.

Adult moths have very specific physical traits and behaviors. Their wingspan varies, but they generally have a stout body. The forewings are relatively narrow and elongated. Most moths have white wings peppered with black spots, known as maculation. These black spots can sometimes be gray or brown. In some rare cases, the pattern is a mix of brown and black. The amount of black speckling changes between individuals. Some moths have almost no black, while others appear almost entirely black.

During the day, moths rest on trees to hide from birds. They prefer specific spots like the underside of branches or tree trunks. Males and females emerge from their pupae between late May and August. Males usually emerge slightly before females. This timing is a common result of sexual selection.

There are several different color forms, or morphs, within this single species. These morphs are controlled by genetics. In continental Europe, there are three main types. The first is the white morph, called typica. The second is the dark melanic morph, called carbonaria. The third is an intermediate form called medionigra. In Britain, the intermediate form is called insularia. North America has its own black morph named swettaria. It is important to note that these are not different species. All these morphs can interbreed and produce fertile offspring. The dark color in many areas is caused by a dominant allele. This means the trait for being dark is passed down easily.

The history of the peppered moth provides a clear look at evolution. In 1887, Edward Bagnall Poulton wrote about how the moths use countershading. Countershading is a type of camouflage that makes an object look flat. Before the Industrial Revolution, most moths were the light-colored typica form. They were well-camouflaged against light-colored trees and lichens. However, heavy pollution in England changed the environment. Soot from factories turned tree trunks black and killed many lichens. This made the light moths easy for birds to see. Consequently, the dark carbonaria morph began to flourish. The first carbonaria moth was recorded by Edleston in Manchester in 1848.

Researchers have worked hard to prove why these changes happened. Bernard Kettlewell conducted predation experiments to study this process. He established that birds were the main force of selection. Birds would eat the moths that did not match their background. This process of genetic darkening due to pollution is called industrial melanism. Modern studies have even looked at how moths see the world. Using ultraviolet cameras, researcher Michael Majerus showed that typica moths reflect ultraviolet light. This helps them blend in with crustose lichens. This camouflage works in both human-visible light and ultraviolet light.

The peppered moth remains a vital link in understanding biological systems. Its evolution is tied to human activity and environmental health. As air quality has improved, light-colored moths have become common again. This shows how quickly populations can respond to new conditions. The genetic basis for this change is also well-understood. The mutation for melanism is caused by a transposable element. This element moves into a specific part of the cortex gene. This change increases the amount of cortex transcript in the developing wings. By studying these tiny insects, we learn how the entire natural world adapts to change.