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Moths, Camouflage and Evolution

Posted: Thursday 6th July 2017 by Twheatear

Three moths with different approaches to camouflage

Some of the ways moths avoid getting eaten...

This week our moth trap produced its first peppered moth. A relatively common species, but famous because its development over the past two centuries is one of the most visible examples of evolution in action.

Most peppered moths nowadays are, like ours, white with black speckling. This makes them hard to find when they spend the day resting on lichen-covered tree branches. But industrial pollution in the 19th and 20th centuries made that much less effective by killing lichens. Particularly around large cities, tree branches were instead mostly black with soot. Resting on one of those trees, a "normal" peppered moth would have been an obvious meal for a hungry bird.

However, as with many moth species, a genetic mutation exists that produces a much darker version. In normal circumstances a large, black, obvious peppered moth has a low chance of surviving to breed, but the industrial revolution changed that. Around Manchester and other industrial cities, suddenly it was this carbonaria form that was well camouflaged and more likely to produce offspring. As a result the, now favourable, genetic mutation quickly came to dominate the moth population in those areas. Reduced air pollution from the late 20th Century is allowing trees to return to their natural colour and lichen coverage, genetically speckled peppered moths are more successful, and the black form is, once again, rare.

Our peppered moth wasn't particularly well camouflaged on the garden table but the mottled beauty on the fence was making a good attempt at invisibility even on a processed wood background. To enhance the effect, these moths press their wings tightly against the surface so they don't cast a shadow. The third moth - one of our favourites - takes the opposite approach: if you want to look like a broken twig then you need to cast a shadow. So buff-tips stand proud of the surface, with wings wrapped into a cylinder.

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