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The pale peppered moth is camouflaged on lichen-covered bark. During the Industrial Revolution, pollution killed the lichen and soot blackened the trees, and a dark form became common in the UK. After clean air laws the lichen returned and pale moths became common again.

This is one of the most famous textbook examples of evolution by natural selection. A 2018 study tested it again: models of bird vision (including ultraviolet, which most birds can see but we cannot) and artificial moths placed in woodland showed that pale models had a 21% higher chance of not being eaten by birds in today's cleaner woods.

Countershading was proposed over 100 years ago by Abbott Thayer. A 2016 field test put hundreds of paper 'caterpillars' with a mealworm inside on bramble bushes for birds: a sharp dark-to-light change worked best in direct sun, a smooth gradient worked best in shade and on cloudy days. The best camouflage depends on the light.

Experiment: A predation experiment with paper moths

1. Cut 20 'moths' (about 3 cm wide) from plain white paper and 20 from newspaper.
2. Fix 10 of each kind at random positions on the newspaper board, and 10 of each on the white board.
3. A 'predator' who has not seen the boards has 15 seconds per board to remove as many moths as possible, one at a time.
4. Record how many of each kind survived on each board. Repeat with at least four different predators and pool the class data.
5. Calculate the proportion surviving for each kind on each board, and the difference in percentage points.
6. Estimate the uncertainty: how much does the result change from one predator to the next? Would 10 moths per kind be enough to convince a scientist?

Moth and board	Survived (out of 10), predator 1	Predator 2	Predator 3	Predator 4	Mean proportion surviving
White moth on newspaper	Prediction
Newspaper moth on newspaper	Prediction
White moth on white board	Prediction
Newspaper moth on white board	Prediction

Questions

1. Explain, in four steps, how natural selection can make the dark form of the peppered moth more common.

2. Made-up data: 15 of 50 white paper moths and 40 of 50 newspaper moths survived on a newspaper board. Calculate the proportion surviving for each kind and the difference in percentage points.

3. Give two reasons why the result of a classroom paper-moth experiment is uncertain.

4. Why might the snowshoe hare's camouflage become a problem as winters get shorter?

Sources for every fact on this sheet: echoesof.science/school/camouflage/sources/

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