The peppered moth, scientifically known as Biston betularia, is a common species of night-flying moth found across temperate regions, including parts of Asia, Europe, and North America. This moth is characterized by its mottled wing patterns, which typically feature a pale background speckled with dark markings, giving it a “peppered” appearance. Peppered moths are relatively small, usually measuring between 1.5 to 2.5 inches across their wingspan. They are solitary insects, generally resting on tree bark during the day and becoming active at night.
Key Predators of the Peppered Moth
Adult peppered moths face a variety of predators, primarily insectivorous birds that hunt during daylight hours. Common bird species known to prey on peppered moths include robins, nuthatches, and flycatchers. These birds actively search for moths resting on tree trunks and branches. Experiments have shown that birds are significant agents of selection, preying on moths that do not blend well with their background.
At night, when peppered moths are active and in flight, bats become their primary predators. Bats rely on echolocation to locate and capture flying insects. While camouflage is less effective against sonar, a moth’s color may still play a role in evading a bat’s detection. Beyond birds and bats, other insectivorous invertebrates, such as spiders, may also capture resting or flying moths.
How Camouflage Protects Peppered Moths
Camouflage is a primary defense mechanism for peppered moths, allowing them to blend seamlessly with their environment to avoid detection by predators. The typical light-colored peppered moth, known as typica, is speckled with black, providing effective camouflage against lichen-covered tree trunks. This coloration makes it difficult for visually hunting predators, especially birds, to spot them.
A darker, nearly black form of the moth, known as carbonaria or melanic, arose due to a genetic mutation. During the Industrial Revolution, pollution blackened tree trunks with soot and killed off light-colored lichens, making the light-colored moths highly visible. In these darkened environments, the melanic moths were better camouflaged and thus had a survival advantage, leading to a rapid increase in their population. As air quality improved, the trees became lighter again, and the light-colored moths regained their camouflage advantage.
Predation Across the Moth’s Life Stages
Predation is not limited to the adult stage; all life stages are vulnerable. Female peppered moths lay eggs in clusters. These eggs can be preyed upon by various small insects or mites.
After hatching, the larvae, or caterpillars, feed on tree leaves. Peppered moth caterpillars are twig mimics, capable of adjusting their body color to match the branches they are feeding on. Despite this camouflage, they are preyed upon by insectivorous birds, predatory beetles, and parasitic wasps.
Pupae overwinter in the soil or in bark crevices. They can be found by ground-dwelling predators such as shrews, rodents, or ground beetles.
Ecological Role of Predation
Predation plays a role in the ecology and evolution of the peppered moth. The selective pressure exerted by predators, particularly birds, directly influences the moth’s population dynamics and distribution.
This selective pressure is evident in industrial melanism, where environmental changes led to shifts in moth coloration as a direct result of predator foraging behavior. The peppered moth serves as a food source within its ecosystem, contributing to the flow of energy through the food web.
Predation ensures that individuals with less effective camouflage are removed from the population, promoting the survival and reproduction of better-adapted moths. This dynamic interaction between predator and prey demonstrates natural selection shaping species over time.