Every fact in the three camouflage lessons is listed here with where it comes from. The numbers in [brackets] on the lesson pages link to this list.
How we rate sources
High: space agencies (NASA), peer-reviewed open textbooks (OpenStax, Rice University) and professional scientific societies (American Physical Society).
Medium-high: reputable science news reporting directly on a primary document.
Medium: single-author essays and popular history sites. We only use these for history details, and never on their own: each one is paired with a second source.
Wikipedia was not used as a source. Numbers are rounded (for example 9.8 m/s² for Earth's gravity). The text was drafted with help from AI (Claude) and then checked against these sources. Corrections: hello@echoesof.science.
Where the facts are simplified or less certain: the groups used here (background matching, disruptive colouration, countershading, warning colours, mimicry) overlap, and one animal can use several tricks at once [2]. The survival figures (21% for pale artificial moths [4], 7% per week for white hares on snowless ground [7]) come from single studies in particular places and are reported as the universities and agencies summarised them; we do not know from these summaries whether they are absolute or relative differences, so the lessons do not calculate with them directly. The paper-caterpillar and paper-moth experiments use children as 'predators'; birds see differently from people (many see ultraviolet) [4], so the classroom results are a model, not proof. The calculations in the 15–16 lesson use made-up class data.
All sources
[1] Protective coloration
Britannica (Britannica School / Kids, student encyclopedia) · Reliability: High
Type: Encyclopedia article for students
Some colouring disguises an animal so that it is less visible to predators or prey. A fawn's spotted coat blends with the forest floor; the decorator crab attaches algae and debris to its shell; some groupers rest motionless on the sea floor. Disruptive colouration (spots, stripes) breaks up the outline, as in the cheetah, tiger, leopard and boa constrictor. Countershading: lighter underneath and darker on top, which offsets the effect of light from above; many marine animals use it so they do not look like silhouettes from below. Varying hares are white in winter and turn brown as the snow goes; some lizards match their surroundings; the octopus changes colour when frightened. Warning colours (often red, black and yellow) advertise defences; the monarch's orange and black pattern goes with a bad taste. A harmless animal may copy the warning colours of a dangerous one, and several noxious species may share similar warning colours so predators learn to avoid them all.
Oxford University Museum of Natural History · Reliability: High
Type: University natural history museum (article)
Stick insects resemble a twig and leaves; animals mimic the bark or leaves they rest on. Mantids blend into their habitats and also have eye spots and red warning colouration. Females of the African butterfly Papilio dardanus mimic distasteful species to trick predators. Alfred Russel Wallace argued that insects deterred predators by resembling other, inedible species. Some snakes have tails that mimic their heads. Mimicry is found in sounds and smells as well as looks.
University of Bristol (news, 31 October 2016; paper in PNAS) · Reliability: High
Type: University research news on a peer-reviewed paper
Abbott Thayer proposed over 100 years ago that animals are darker on their backs to hide their 3D shape. Light from above makes a uniformly coloured animal lighter on top and shadowed below; countershading cancels these shading cues. Researchers pinned hundreds of caterpillar-sized paper tubes, printed with green shading and each holding a dead mealworm, on bramble bushes in Bristol parks and recorded how many birds took. A sharp change from dark back to light belly worked best in direct sun; a smoother change worked better in shade and on cloudy days.
University of Exeter (news, 17 August 2018; paper in Communications Biology) · Reliability: High
Type: University research news on a peer-reviewed paper
The pale peppered moth is camouflaged against lichen on tree bark. During the Industrial Revolution pollution killed lichen and soot darkened the bark, and a dark form became common in the UK; after clean air laws the lichen recovered and pale moths became common again. Birds such as sparrows, great tits, blue tits, robins and blackbirds are key predators. Researchers simulated bird vision (including ultraviolet, which most birds see and humans do not), used museum specimens including some from Bernard Kettlewell's 1950s collections, and placed artificial moths in woodland, mostly in Cornwall: lighter models had a 21% higher chance of not being eaten. The peppered moth is one of the most famous textbook examples of evolution by natural selection.
Smithsonian Ocean (Smithsonian Institution) · Reliability: High
Type: National museum (ocean education portal)
Squid, octopuses and cuttlefish can change skin colour in the blink of an eye. Thousands of chromatophores lie under the skin; each has an elastic sac full of pigment, and nerves and muscles control whether the sac is expanded or contracted. Iridophores have stacks of reflecting plates that make iridescent greens, blues, silvers and golds; leucophores mirror the colours of the surroundings. Octopuses can also change the texture of their skin with small projections called papillae, making them nearly invisible. Colour is also used to signal: male Caribbean reef squid change colour to attract females and repel rivals; the blue-ringed octopus shows its blue rings as a warning.
U.S. National Park Service (Rocky Mountain National Park) · Reliability: High
Type: National park agency (species page)
The summer coat is greyish-brown on top with a whiter chin, tail and belly; the winter coat is mostly white with black rims on the ears. Day length triggers the change, which happens over about 70 days. The large hind feet act as snowshoes and fur on the soles gives insulation and grip on snow.
[7] Can camouflage keep up with climate change? Connecting climate projections to adaptation for the snowshoe hare
U.S. Geological Survey (Climate Adaptation Science Centers) · Reliability: High
Type: National science agency (research project page)
In response to changes in day length, snowshoe hares moult from brown to white for winter. Shorter snow seasons leave hares white before it snows, making them more visible to predators; mismatched white hares on snowless ground had a 7% higher chance of being killed each week. Hares did not readily change their hiding or fleeing behaviour and cannot readily adjust their moult to shorter snow seasons. Snowshoe hares make up 96% of the diet of the threatened Canada lynx in western Montana.