malformalady:

Industrial Melanism. Many animals have a body colour that allows them to blend in with their background. Such as moths with speckled wings that camouflage them when resting on lichens. However, in heavily industrialized areas, pollution results in trees and structures being covered in a layer of soot. This layer means that light coloured insects resting on dark backgrounds can be easily spotted by predators. This results in fewer light coloured individuals in the population and breeding between the darker form results in more dark forms. Over time there become many more dark forms of a species in the environment than the light form. This is known as Industrial melanism.

(via fuckyeahentomology)