Peppered moths (Biston betularia) are commonly found across the majority of the United Kingdom. They have both a pale and a dark form, which can be found in different concentrations according to environmental factors. These moths are often used as an example of natural selection at work.
Pale Coloration
The pale coloration is the typical coloration of a peppered moth -- also known as typis. Moths of this color are mottled black and white, with a salt-and-pepper appearance. This color is perfect for camouflaging the moths on their favorite type of tree -- the birch tree -- the trunks of which are pale and covered in types of fungus called lichens. The camouflage makes them less likely to be spotted, and subsequently eaten, by predators.
Dark Coloration
In addition to the typical coloration, there is also a natural genetic mutation in peppered moths that causes them to be almost entirely black in color. This variation is known as carbonaria, or the melanic variation. Under normal environmental conditions, this coloration means the moths are poorly camouflaged, but there are times in which it's useful.
Colors and Natural Selection
During the industrial revolution, peppered moths underwent a drastic change in common coloration that highlights the way natural selection works. Prior to the industrial revolution, the pale color variation had been the most common, with the dark variation occurring only rarely. However, with so many factories being built, the trunks of trees in larger cities began turning black with soot. Now the melanic variation had a distinct advantage over the paler moths, as they were better camouflaged on the birch trees. Within 50 years of the first dark peppered moth being recorded in Manchester, 98 percent of the peppered moths in the city were of the melanic variation. Following the clean air act of 1964, soot deposits have dramatically declined, and black peppered moths have declined with them.
Other Adaptations
Peppered moths have some other useful adaptations to help them survive. While many moths and butterflies can only lay their eggs on one type of plant, this species can lay on several, including hawthorne, birch, lime and rose. This gives them more options if one type of plant starts to decline. Additionally, while they're in their larval -- or caterpillar -- form they look remarkably like sticks or twigs, which offers them camouflage from potential predators.
