Peppered moths avoid predators primarily through camouflage, blending their wing patterns into the tree bark where they rest during the day. But their survival strategy goes well beyond simply looking like bark. These moths actively choose where and how to position themselves, and even their caterpillars can change color to match the twigs they sit on.
Wing Patterns That Disappear Into Bark
The typical peppered moth has pale, speckled wings that closely resemble lichen-covered tree bark. This cryptic coloration makes the moth nearly invisible to the birds that hunt it. At least nine bird species are known to eat peppered moths, including robins, great tits, blue tits, blackbirds, starlings, and even woodpeckers. All of these birds hunt by sight, so visual camouflage is the moth’s primary line of defense.
How effective is this camouflage? In controlled experiments, pale moths resting on pale, lichen-covered bark had a 21% greater survival advantage against bird predation compared to dark moths on the same background. That margin is large enough to shift an entire population’s genetics over just a few generations.
Moths Choose Their Position Carefully
Camouflage isn’t just about color. Peppered moths actively orient their bodies on tree trunks to align their wing patterns with the grooves and furrows in the bark. They typically position themselves roughly perpendicular to the direction of the bark’s furrows, which makes the lines on their wings flow seamlessly into the lines on the tree. The result is a near-perfect visual match that makes the moth’s outline disappear.
What’s remarkable is how they pull this off. Researchers found that moths detect the three-dimensional structure of bark through touch, then use that tactile information to position themselves for visual camouflage. Even when the visual pattern of the background was altered experimentally, the moths still relied on the physical texture of the surface to choose their resting orientation. They’re essentially feeling their way into the best hiding spot.
Caterpillars That Change Color
Adult moths aren’t the only life stage with impressive camouflage. Peppered moth caterpillars masquerade as twigs on their food plants, and they can change color to match the specific twigs they rest on. Larvae resting on brown twigs turn brown. Those on green twigs turn green. And rather than simply switching between two fixed colors, the caterpillars produce a continuous range of intermediate shades, fine-tuning their appearance to approximately match whatever background they’re sitting on.
When researchers placed caterpillars in mixed environments with twigs of different colors, the larvae didn’t settle on some average, in-between shade. Instead, each individual specialized its color toward one specific twig color, committing to the best match for its chosen resting spot. The caterpillars use visual cues to drive these color changes. Experiments that held diet and texture constant but varied background color confirmed that the larvae were responding to what they could see around them. Since birds heavily prey on caterpillars that don’t match their surroundings, this color-changing ability provides a real survival benefit.
The Genetics Behind Dark and Light Forms
Peppered moths exist in two main forms: the pale, speckled “typica” form and the dark “carbonaria” form. The dark coloring comes from a specific genetic change: the insertion of a chunk of repetitive DNA (called a transposable element) into a gene called cortex. This inserted DNA increases the activity of the cortex gene during early wing development, which ramps up dark pigment production. The result is wings that are almost entirely black.
This single mutation is what gave rise to the famous case of industrial melanism. During the 1800s, coal pollution killed the pale lichens on trees across industrial Britain and coated bark in dark soot. Suddenly, the pale moths were conspicuous against dark, bare trunks, while the dark form blended in perfectly. By the mid-20th century, over 90% of peppered moths in heavily polluted regions of northern England were the dark carbonaria form. In cleaner areas to the west, that figure stayed below 5%.
How Clean Air Reversed the Trend
As air quality improved across Britain following clean air legislation, lichens grew back on trees, and bark surfaces lightened. The survival advantage flipped back in favor of the pale form. By the 1980s, the zone where dark moths made up 90% of the population had shrunk to just northern England. The decline continued steadily. Today, the dark form accounts for less than 50% of the population even in its former strongholds, and in most areas it’s dropped below 10%. Similar declines have been documented across Europe and North America.
This reversal is one of the clearest real-world demonstrations that camouflage drives survival in peppered moths. When the background changed, predation patterns shifted, and population genetics followed. The moths that matched their environment survived long enough to reproduce. The ones that didn’t were picked off by birds.