Industrial Melanism

The Peppered Moth, Biston betularia, is one of the most important moths of the 20th century.

In the 1950s, Bernard Kettlewell wanted to explore why the Peppered Moth had evolved from its traditional peppered form to a much darker morph. The change had occurred since the industrial revolution and Kettlewell’s experiments sought to demonstrate that the moth had evolved to adapt to its changed environment. The soot emitted by factories in the industrializing country was coating the moth’s habitat so that its white ground form made it much more obvious to predators. Evolving to a dark or black form allowed the moth to become camouflaged once again. This was industrial melanism. The Kettlewell experiment is described in Wikipedia and it is well worth clicking through. I think I have read books in the past that challenge the integrity of Kettlewell’s methods but of course the moth has now reverted to its original form as the pollutants have been progressively removed from the atmosphere. So whatever the possible flaws in the methodology, Kettlewell’s experiments appear to stand up. This is evolution in action roughly within my lifetime. So if you see one of these, just reflect for a moment on how important it was back in the 1950s. BistonbetulariaI photographed it on a lichen-covered brick in our terrace simply to illustrate how well it blends in.

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21 thoughts on “Industrial Melanism

  1. Studying this moth was one of the highlights of my college career~fascinating. How good it is to see the lighter form able to flourish now.
    A few years ago I got a lesson in air quality. In Illinois the air is quite clean, due to regulations on factories and car emissions. This isn’t nation-wide, it turns out. When I traveled to Washington State I got a whiff that took me right back to the dirty 70’s. Nostalgia is fun but it was startling to be confronted with the issue of air quality that starkly. As you say, we have seen big changes in our lifetime.

    • We left HK in part because of the air quality. It is not as bad as Beijing but it is like the frog in boiling water. You don’t notice the change until it is too late. People complain about the air here but our trees are smothered by lichens – a good bio-indicator of air quality. Let’s hope the Light form of Biston betularia continues to dominate.

    • If it isn’t a word it ought to be Jenny. Most mornings I find something to enjoy – cockchafers don’t qualify – and they fill a niche when I am not busy with birds or dragonflies.

  2. Nature is wondrous and this is an interesting example of a type of evolution. I have noted however that birds and animals adapt to changes in the environment thus enabling survival of the species.

    White winged dove, Inca dove and House Finch are just three examples of habitat adaptation that expanded their breeding range in Texas. Other species decline and remain the same. It’s cause for the question of why some things adapt and why others can not.

    But this is off topic and I’ll stop here but this one factor would make for some interesting posts from you about the decline or the increase of some species of birds in GB.

    • I will think about that topic Yvonne. However I am not sure I have the depth of knowledge. In some instances there are no certain answers why species are declining. The broad assumptions are habitat loss, pesticides and climate change. I am deeply concerned about the humble House Sparrow here. Tree Sparrow numbers have already plummeted and now its urban counterpart is falling fast. Lots of theories but none proven.

  3. If that theory is followed through we will soon have moths that will be shaped and coloured like people holding Iphones.
    There are lots of sparrows here still, and bees.

  4. I studied this moth in college also. Very interesting about adaptation. I do love to observe why things are declining and or flourishing here. Our/your imported house sparrows are in abundance here. Not as many predators. However, they cause our native bird populations to drop as they kill our bluebirds and compete with nesting sites.
    These adaptations are sometimes a simple answer (pollution) or sometimes a complex puzzle.

  5. I was reading Noelle’s blog recently and she bred moths for the film ‘Silence of the Lambs’ fascinating, as long, as I said, that they stay outside! I think it’s the hairy look of them because I quite like holding butterflies.

  6. I’d read that story before and was just as amazed reading it once again. The animal Kingdom (or Queendom) is quite adept at doing what is necessary for survival of the species. Too bad our own species is at such a loss for survival. But not to worry…we’ll probably destroy ourselves before adaptation becomes necessary.

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