Garden Robin

Garden Robin

Thursday 28 May 2015

Peppered Moth




A Peppered Moth (Biston betularia)was in the moth trap yesterday morning - another new species for the year.




This species provides a good example of evolution by natural selection in action.

Peppered Moths are usually white with black speckles covering the wings. These markings make them well camouflaged against lichen covered trees and walls where they rest during the day. A genetic mutation in some moths results in them being melanic (i.e. they have black wings). The black form is not well camouflaged against a lichen covered tree, wall or fence and are, therefore, far more likely to be eaten by predators, such as birds. Under normal environmental conditions fewer of the black type survive to breed and they are, thus, far less common.

During the nineteenth century, following industrialisation, it was noticed in towns and cities that the black form of the moth was becoming more common than the peppered form. The Industrial Revolution and increasing number of coal fires led to the atmosphere becoming increasingly polluted killing off lichen and blackening the tree trunks. The melanic form of the moth was now better camouflaged from predators than the peppered form and thus more likely to survive and breed. As moths are short-lived evolution by natural selection happened quickly.

In the mid twentieth century measures were introduced to control and reduce air pollution and the air in cities and towns became cleaner. Lichens re-colonised tree trunks and walls and the melanic form was now at a disadvantage and more likely to be killed and eaten. The situation now reversed and once again the better camouflaged peppered form of the moth became more abundant in cities.

Unfortunately, the species is now declining and the numbers of Peppered Moths had declined by two thirds between 1968 and 2002 - the reasons for the decline are unknown.

8 comments:

  1. I've read about this moth and it's one of those marvels of nature and evolution. Glad you found a new species for this year. :-)

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    1. Thanks so much. I love this moth - I mainly trap noctuids so any geometrid moth is cause for celebration :)

      I think there were some flaws in the original Kettlewell experiments and further research was undertaken by Michael Majerus of Cambridge Uni but this more or less confirmed the basic elements of Kettlewell's findings were correct.

      Was typing up a job application form and letter etc. for son last night (being able to copy type has huge disadvantages at times!!!) inbetween doing this post so didn't have time to re-check the results of Majerus's work! There is loads on internet if you google it particularly link to Miller and Devine. http://www.millerandlevine.com/km/evol/Moths/moths.html

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  2. What a lovely looking moth, I remember my son covering this subject when he was at school.
    No moths in my trap, but noticed one I had not seen before on the wall in the garden, got camera as it flew on to a tub, took a quick shot as it flew of, then three sparrows came from no were and took it out...! great to watch but not good for the moth. I really should have caught it and released it later.
    Amanda xx

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    1. Thanks Amanda. I've had problems in the past with blackbirds, robins and house sparrows hovering as I empty the trap. I try very hard not to think how many are gobbled up from around the trap at dawn (hours before I get up!!). Have you identified the moth yet from your photo?

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    2. Have put moth photo on iSpot, don't think it's a good enough photo for ID.. Wanted to ask, do you put "water" ie, damp sponge for your caterpillars, have changed the food daily and to day cleaned the whole lot out (rid of poo !).
      Amanda xx

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    3. Hope you get a moth id.

      I think caterpillars get all the moisture they need from the leaves. I do spray my stick insects' bramble with water daily but I never did the same with the Emperor moth caterpillars. Just put in new food as and when necessary and cleaned them out. Oh!! and I used to talk to them :)

      When they near the time to pupate you need to put in sticks or some soil at the bottom of the container whichever they use to pupate on/in.

      Good luck with them. Still can't make up my mind whether or not to accept some more Emperor moth eggs/caterpillars. I don't think now any of my females will emerge this year so will have to wait and see what happens next Spring!

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  3. Always one of my favourite moths with a particularly fine looking specimen to illustrate this fascinating post. The 'normal' Peppered type tend to dominate here and I have only trapped the black form once, though it will be interesting to see which type dominates up at Grosmont, especially what with all the soot and stuff from the steam trains!

    Kindest regards & best wishes :-)

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    1. They are lovely moths David. I've never caught the black form here but it will be really interesting to see which type dominates when you move to Grosmont!

      Best wishes Caroline

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