The peppered moth, Biston betularia, is a night-flying species famous for the phenomenon of industrial melanism. Its life cycle includes a distinct larval stage, the caterpillar, which is responsible for the insect’s primary period of growth and feeding. The larva consumes vegetation, prepares to overwinter, and eventually emerges as the adult moth. Understanding the caterpillar’s diet and habits reveals a complex interplay between its feeding needs and its defense strategies.
Primary Diet: Generalist Herbivores
The peppered moth larvae are known as polyphagous, meaning they are generalist herbivores capable of feeding on a wide variety of plants. Their diet consists almost entirely of the foliage from numerous deciduous trees and shrubs found across the northern hemisphere. This broad palette of food sources is a significant factor in the moth’s widespread distribution and ecological success.
Common host plants include species like birch, oak, willow, alder, and lime, but their consumption extends to many others, such as hawthorn, blackthorn, and even rose bushes in garden settings. The caterpillars primarily feed on the leaves of these woody plants throughout the summer and early autumn. This flexible feeding habit allows the larvae to thrive in diverse habitats, including woodlands, hedgerows, and urban parks.
The ability to consume leaves from a diverse range of plant species provides a major advantage, especially where dominant tree species vary. Larvae also feed on smaller plants like bramble and hop, further demonstrating their adaptability. This generalist diet is closely linked to their camouflage, allowing them to settle and feed in a wide array of visual environments.
Feeding Strategy and Habitat Selection
The peppered moth caterpillar employs a specific feeding and resting strategy that integrates its nutritional needs with its highly effective anti-predator defense. The larvae are primarily nocturnal feeders, consuming the leaves of their host plants under the cover of darkness. This pattern of activity helps to minimize their exposure to visual predators, particularly birds, which are most active during the day.
During daylight hours, the caterpillars stop feeding and adopt a stationary posture on the twigs and branches of their food source. Their body shape and coloration are highly specialized for masquerade, a form of camouflage where they physically resemble an inanimate object, specifically a small twig or petiole. The larvae often possess a deeply cleft head and wart-like structures, which enhance their imitation of a broken stem or bud.
The larvae exhibit color plasticity, changing their body color to match the specific twig they are resting on, ranging from green to various shades of brown. Research suggests that the caterpillars can visually sense the color and luminance of the background using their skin. This visually induced color change is a continuous response, allowing them to maintain a strong visual match to the branch, whether it is birch or oak.