The peppered moth, Biston betularia, is an insect species found across various ecosystems in the Northern Hemisphere, including Europe and North America. Present in diverse habitats like shrublands, parklands, and forests, it serves as a food source for a range of animals, contributing to the ecological food web.
Birds as Primary Hunters
Birds are primary predators of peppered moths. Many common insect-eating birds, such as robins, great tits, flycatchers, and nuthatches, include peppered moths in their diet. These visual predators hunt during daylight, spotting moths resting on tree trunks and branches. The effectiveness of a moth’s camouflage directly influences how easily birds can locate and capture them, playing a substantial role in the differential survival of peppered moth color forms.
Other Natural Enemies
Beyond birds, other animal groups also prey on peppered moths. Bats are significant nocturnal predators, using echolocation to locate flying moths in the dark. Moths possess specialized hearing organs that can detect the ultrasonic sounds emitted by bats, allowing some species to initiate evasive maneuvers. This ongoing predator-prey interaction has led to an evolutionary “arms race” between bats and moths.
Other opportunistic predators include spiders, which may capture resting moths in their webs or through active hunting. Some predatory insects and small mammals might also consume peppered moths, although their impact is generally considered less widespread or consistent compared to birds and bats. These varied predators contribute to the overall pressures faced by peppered moth populations across their habitats.
Environmental Influence on Predation
The effectiveness of a peppered moth’s camouflage is influenced by its environment. Peppered moths exhibit different color forms, primarily a light, speckled morph and a dark, melanic morph. The light morph is well-concealed against lichen-covered tree trunks, which are common in unpolluted areas. In contrast, the dark morph blends more effectively with tree bark that has been darkened by soot or pollution.
Environmental changes, such as industrial pollution, directly affect tree bark coloration and the presence of lichens. During the Industrial Revolution, soot from factories blackened trees, making light-colored moths more conspicuous to visual predators like birds. This shift in background color altered the success rate of predation, favoring the survival of the dark morph in polluted environments.
Predation’s Evolutionary Impact
Predation by various animals has had a significant evolutionary impact on the peppered moth. Predators act as a selective pressure, influencing which moth forms are more likely to survive and reproduce. The differential survival rates of light and dark morphs, depending on their environmental background, illustrate the concept of natural selection in action. For example, in polluted areas, dark moths were better camouflaged and less likely to be eaten, leading to an increase in their numbers.
Conversely, in cleaner environments where lichens returned to tree bark, the light morph gained a survival advantage, leading to a decrease in the dark morph’s frequency. This observable change in the genetic makeup of peppered moth populations over time, driven by predator-mediated selection, provides a well-documented example of rapid evolution. The interaction between the moths and their predators highlights how environmental factors can shape the characteristics of a species.