The peppered moth, Biston betularia, is a well-known insect found across Europe and North America. These moths are primarily nocturnal. During the day, they typically rest on surfaces such as tree bark and branches. Their presence in various environments, including woodlands, parks, and gardens, makes them a common sight.
Predators of Peppered Moths
Peppered moths face a range of predators, both during the day and at night. Birds are significant daytime predators, with species such as flycatchers, nuthatches, and European robins frequently preying on resting moths. These birds rely on their keen eyesight to spot moths against tree bark, making camouflage a primary defense for the moths.
At night, bats become their main hunters. Bats use echolocation to navigate and locate flying insects in the dark, making it challenging for moths to evade detection based on visual camouflage alone. Beyond birds and bats, other invertebrates also prey on peppered moths. These include spiders, which may ambush moths in their webs, and predatory insects like praying mantises and certain beetles.
Camouflage and Predation
Camouflage is an important survival strategy for peppered moths, influencing their vulnerability. Their wing coloration allows them to blend seamlessly into their environment, particularly the bark of trees and lichens. This ability to match their surroundings helps them avoid detection by visually hunting predators like birds.
Peppered moths exhibit two primary color forms: the light, speckled form known as typica, and the dark, melanic form called carbonaria. The effectiveness of each form’s camouflage depends on the specific environment. Light-colored moths are well-hidden on lichen-covered tree trunks, while dark moths find concealment on soot-darkened trees. This adaptation makes it harder for predators to spot them, affecting their survival rates.
Ecological Impact of Predation
Predation by birds and other animals exerts strong selective pressure on peppered moth populations, driving natural selection. Historically, changes in environmental pollution, particularly during the Industrial Revolution, impacted the prevalence of the moth’s different color forms. As soot blackened trees and killed lichens, the light-colored moths became more visible and were preferentially eaten by birds.
This shift led to a rapid increase in the dark-colored carbonaria form, which was better camouflaged against the darkened trees. When pollution levels decreased due to clean air legislation, the environment gradually returned to its lighter state, and the lighter typica form once again gained a survival advantage. This demonstrates how predation is a force shaping the moth population’s traits over generations, highlighting evolution in action.