School › Camouflage › Ages 15–16
Camouflage and natural selection
From the peppered moth to snowshoe hares in a warming climate: how camouflage evolves, how cephalopods change colour, and how to analyse a predation experiment with proportions and uncertainty.
Read
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.[4]
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.[4]
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.[3]
Snowshoe hares moult from brown to white in response to day length, over about 70 days. With shorter snow seasons, hares are now often white before the snow comes; mismatched hares had a 7% higher chance of being killed each week, and they did not readily change their behaviour to compensate.[6][7]
This matters for whole food webs: in western Montana, snowshoe hares make up 96% of the diet of the threatened Canada lynx. Whether hare camouflage can evolve fast enough to match the climate is an open research question.[7]
Cephalopods change colour within a single lifetime rather than over generations. Each chromatophore is an elastic sac of pigment opened or closed by nerves and muscles; iridophores (stacks of reflecting plates) add iridescent colours, leucophores mirror the surroundings, and papillae change the skin's texture.[5]
Try it: A predation experiment with paper moths
You need
- White paper and old newspaper
- Scissors
- Sticky tack
- Two large boards or sheets: one covered with newspaper, one plain white
- Stopwatch
- Calculator
Safety
Use scissors carefully. Predators remove moths with their fingers only, no pins. Keep the boards flat on a table so nothing falls.
What to do
- Cut 20 'moths' (about 3 cm wide) from plain white paper and 20 from newspaper.
- Fix 10 of each kind at random positions on the newspaper board, and 10 of each on the white board.
- A 'predator' who has not seen the boards has 15 seconds per board to remove as many moths as possible, one at a time.
- Record how many of each kind survived on each board. Repeat with at least four different predators and pool the class data.
- Calculate the proportion surviving for each kind on each board, and the difference in percentage points.
- 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?
What happens, and why?
Moths that match their background survive better because predators that hunt by sight find them more slowly. Over many generations, the form that survives and reproduces more often becomes more common: natural selection. Real studies need large samples, real predators and an understanding of how those predators see, which is why the 2018 peppered moth study modelled bird vision, including ultraviolet.[4][3]
Play: One life or many generations?
Does this change happen within one animal's life, or does it build up over many generations? Sort each one.
Your best score is kept only on this device. Nothing is sent anywhere.
Quiz
Other ages: Ages 6–7 · Ages 10–11