Nature on our Doorsteps: Evolution in action

THE Peppered Moth has distinctive markings which look like freshly-ground black pepper, scattered over a grey-white surface.

The degree of black speckling can vary, so some individuals appear darker than others.

This speckling acts as a camouflage, helping the moth to blend in against lichens growing on trees and buildings.

This colouring, however, is only one form of the Peppered Moth. In the 19th century, following the British Industrial Revolution, a second form of this moth was discovered in Britain.

It was seen that a pure black form was more plentiful in the cities where buildings and trees became coated in sooty pollution from the many factories.

The Peppered Moth has a sturdy, furry body, and its long, narrow wings are held out to its sides

It was noticed that on these sooty black surfaces, the moth’s lightly peppered form was easily seen and caught by birds, and so this form of the moth decreased in the cities.

In the cleaner countryside however, the lightly speckled form was still well camouflaged on lichens, so its numbers remained steady.

In the polluted cities, the densely speckled forms of the moth did better because they were less easily spotted by predators against the soot.

Over time, these city moths evolved into a pure black form.

This development and spread of the black form of the Peppered Moth is seen as an example of natural selection, or evolution in action.

Nature on our Doorsteps is a weekly column contributed by Rosaleen Dwyer, South Dublin County Council’s Heritage Officer