Industrial melanism is widespread in the Lepidoptera (butterflies and moths), involving over 70 species such as Odontopera bidentata (scalloped hazel) and Lymantria monacha (dark arches), but the most studied is the evolution of the peppered moth, Biston betularia. It is also seen in a beetle, Adalia bipunctata (two-spot ladybird), where camouflage is not involved as the insect has conspicuous warning coloration, and in the seasnake Emydocephalus annulatus where the melanism may help in excretion of trace elements through sloughing of the skin. The rapid decline of melanism that has accompanied the reduction of pollution, in effect a natural experiment, makes natural selection for camouflage "the only credible explanation".
Other explanations for the observed correlation with industrial pollution have been proposed, including strengthening the immune system in a polluted environment, absorbing heat more rapidly when sunlight is reduced by air pollution, and the ability to excrete trace elements into melanic scales and feathers.
In 1906, the geneticist Leonard Doncaster described the increase in frequency of the melanic forms of several moth species from about 1800 to 1850 in the heavily industrialised north-west region of England.
In 1924, the evolutionary biologist J. B. S. Haldane constructed a mathematical argument showing that the rapid growth in frequency of the carbonaria form of the peppered moth, Biston betularia, implied selective pressure.