What is the the story of the peppered moth

10/11/2021

A moth is a moth is a moth. Or is it?

When a moth changes colour based on its surroundings—like the peppered moth—there is perhaps something a little bit special about what is traditionally a very under-loved member of the insect class.

Read on to find out exactly how the peppered moth once changed its appearance—and how it changed back again!

What is the peppered moth?

In 2021, peppered moths look by and large like your average, run-of-the-mill moth. Belonging to the Geometridae family, most peppered moths today have white wings sprinkled with black speckles, though you will find the occasional all black, heavily-spotted moth—but this was not always the case. At the dawn of the Industrial Revolution in the late 18^th century, there was a colour switch, with the predominantly white moths evolving into a melanic black spotted colour. But why exactly did that happen?

The Industrial Revolution

Prior to the Industrial Revolution, white moths would nestle among spotted lichen on tree trunks, branches and twigs to camouflage and therefore, avoid predators. However, widespread industrialisation and the burgeoning use of coal created thick, sooty air pollution, which resulted in burnt and blackened flora. This was bad news for white peppered moths.

No longer camouflaged, the easily seen white insects were picked off by predators from bats to birds to reptiles. This quick elimination of the most lightly coloured moths catalysed industrial melanism, where the more heavily spotted moths survived longer to procreate resulting in the proliferation of darker moths—who were more adept at blending into their surroundings.

It was an accelerated example of natural selection, where the fittest version of a species survives. In this case, it was the black peppered moth.

Black or white peppered moths can camouflage more effectively depending on the surface.

Natural selection

As the white moths were being eradicated by birds and bats, the black moths continued to thrive in relative peace far from their predators’ gaze. Along with the speedy environmental evolution, the short lifespan of moths and fast rate of procreation amounted to an expedited transformation from white to black. The first black peppered moth was recorded in Manchester in 1848, but by 1895—just 47 years later—98% of the moths in the city were of the black peppered variety.

B(l)back to white

As time moved on, machines industrialised and pollution control methods became widespread, the tables were once again turned—black moths began to experience what the white moths had many years earlier. As the lichen and other greenery returned to a lush, pre-industrial state, it was now the black moths that stood out to become easy prey. This, in turn, left the white moths to thrive and produce offspring, driving a reversal in the natural selection evolution that had occurred a century earlier.

While the white peppered moths remain the most commonly found of the two varieties today, there are still some darker black peppered moths in the wild, fighting to defend their place in the animal kingdom.

Chemwatch

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