The Story of the Peppered Moth

Laura Candler: Hands-On Science

The story of the peppered moth began long ago in Manchester, England. Two types of peppered

moths lived there. One was light gray with dark gray speckles. The other was black all over. Until

the 1850’s, there were more light gray moths than dark gray ones.

Peppered moths loved to rest on birch trees. The color of the light gray moths matched the color of the birch bark almost

perfectly. Hungry birds had a hard time finding the light moths. Instead, the birds ate the dark moths which were

much easier to see against the bark of the birch tree.

Between 1850 and 1900, England began to change. Factories were build which pumped tons of black smoke

and soot into the air. The leaves and bark of trees became covered with dark soot. During this time, scientists noticed that almost all the light gray moths had disappeared. Black

moths became the most common peppered moths in England. What caused this change?

Scientists realized that the light gray moths no longer blended in with the birch bark. The birch trees were black with soot. Hungry birds could easily spot any light moths resting on the trees. Now the dark moths blended in with

the bark and were able to escape the birds.

Fewer and fewer gray moths lived long enough to have light colored babies. At the same time, more dark moths survived and had dark baby moths. In less than 50 years,

the number of dark moths became greater than the number of light moths.

But the story of the peppered moth did not end there. After many years, laws were passed to clean up England’s pollution. Factories

were no longer allowed to pump smoke into the air. Slowly the rains washed the dark soot from the trees. What do you think happened to

the numbers of dark and light moths?

 

As you might have guessed, the peppered moth again adapted to its new environment. Light moths began to

survive since hungry birds could not easily find them. Now light colored moths once again outnumber their darker

relatives.

Is it true??? Did this REALLY happen???

The answer is yes and no. The Story of the Peppered Moth is used in almost every biology book out there- especially to teach evolution, however, we are using the story to teach ADAPTATIONS and CAMOUFLAGE. The moths didn’t necessarily die out because of the population, but they have to find other areas to live in order for their species to survive.

Some of the photos you saw were staged with dead moths so that the story would have graphics. It’s a “lie” per se, but it’s not totally telling the truth either.

No new living species can emerge by way of natural selection. The Industrial Revolution moths are an excellent example of this.

Until the last quarter of the 20th century, tree trunks grew darker in color with the pollution of Industrial Revolution.

Therefore, the light-colored moths alighting on these trees became more visible to predators, and since they were more easily caught, their numbers declined. The numbers of dark

moths, however, increased. But this, of course, is not evolution. No new species was formed, and all that happened was a shift in ratios of variation within an

existing species.