15 The Curious Case of the Peppered Moth-Mid

The Curious Case of the Peppered Moth FOCUS Question What caused the peppered moth population to change color twice?

Different Colors When you think of certain animals, a specific color may come to mind Red for a cardinal. Orange for a tiger. However, some species have more than one color that can appear in their population. Most black bears, for example, have an all-black coat of fur. But did you know that not all black bears are black? They can also be brown, cinnamon, or even blond. Other animals also show this kind of variation. A jaguar can have a typical spotted yellow coat or be almost entirely black. Even monarch butterflies, normally orange, are sometimes white instead. These different color types are called morphs.

The Peppered Moth Some species of moths have morphs. One famous example is the peppered moth. This night-flying moth is found in Europe, North America, and many parts of Asia, including Russia and China. The peppered moth comes in two morphs—white and black. The white morph is the typical one, making up about 99 percent of the population. That is why it is called typica. Typica peppered moths look as if someone sprinkled pepper over their white wings and backs. This pattern camouflages the white moths on the trees where they rest during the daytime. They blend in with the light-colored lichen that grows on the trees.

The Moth's Morph Blending in is a good thing for peppered moths since moths are an important food source for birds. But birds have a hard time finding the white moths because they are camouflaged. The black morph is easier to see against the lighter trees. Many of the black peppered moths are eaten before they can reproduce. That is why there are fewer of them. Only 1 percent of the individuals in the species are black morphs. The black morph remained rare in the population for thousands of years. But in the late 1700s, something changed. That's when the case of the peppered moth became curious. Word Wise The root word in carbonaria— carbon—comes from the Latin word carbo, which means "charcoal" or "coal."

Pollution From 1780 to 1830, the urban areas of Great Britain went through a large transformation. Factories and homes in big cities like London and Manchester stopped using wood as their main form of fuel. Instead, they used coal to power steam engines, furnaces, and fireplaces. This time in history became known as the Industrial Revolution. Coal was a plentiful and cheaper source of fuel. But burning it came at a cost. Chimneys belched black fumes—produced by burning coal—into the air. Wind carried the smoke away from cities. The countryside was soon covered in a blanket of black soot.

Suddenly Seen The black soot covered forests and stuck to tree trunks and branches. A toxic gas in the soot, called sulphur dioxide, killed off the light-colored lichens growing on the trees. As a result, the trees turned very dark. The darkened trees were not an ideal place for white peppered moths. Before the pollution, those moths had blended in with the light color of lichens (see page 3). But now they stuck out noticeably against the darkened bark. Think About It Predict how the darkened trees affected the peppered moth population. Then read on to discover the answer.