Moth of the birch

The moth of the birch ( Biston betularia L.) is a Insecte about the Lépidoptère S, of geometrids. It is a night butterfly moderated areas, often quoted like example of adaptation to the evolution of its natural environment by change and Natural selection.

Industrial melanism of the moth of the birch

The moth of the birch meets in two forms, a Morphe of clear color said typica and the other sinks known as carbonaria or melanic , these variations of color being due to the quantity of Mélanine present in the wings of the adult butterfly.

From the 19th century, the Entomologiste S observe that the dark form becomes more frequent near the industrial Ville S of England; observed for the first time in 1848 in the area of Manchester, this dark form became largely majority in 1895 in this same area (more than 98% of the population).

This observation is then brought closer to another phenomenon: because of the Atmospheric pollution by the residues of Combustion of the coal, the trunk S and the Branche S of the Arbre S became darker (at the same time by the deposits of smoke and probably also by the disappearance of the clearer Lichen S which recovered them). However these night butterflies are posed in day on the trees. A certain number of field studies then showed that the Taux of survival of the individuals of the carbonaria type was higher than that of the individuals of the typica type, probably because the latter were more visible with the eyes of their predatory Oiseau X, when they were posed on the trees become darker. However, starting from the end of the Years 1960, this phenomenon is reversed. The form typica becomes again frequent. It is as at this period as efforts are set up to improve quality of the air in Great Britain, efforts which result in particular in a reduction in the deposits of atmospheric pollution on the tree trunks.

Thus, even if the true nature of the multiples pressures of selection to which the moths of birch are subjected remain dubious with the influence of other factors like the role of the mélanine in the Thermorégulation of the butterflies, the quick changes of the melanism within the population of the moths of the birch (which one finds in a similar way and at the same time at other species of butterflies) are regarded as an example particularly striking of the mechanisms of Natural selection related to the Prédation.

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