Field guide · eight patterns

Why do animals have stripes and spots? A pattern atlas

Every explanation of animal patterns answers one of two questions and skips the other. Either it tells you how a zebra's skin grows stripes, with Alan Turing and a pair of chemicals, or it tells you what the stripes are for, with flies and lions, and leaves the growing to someone else. The two answers are different, and an animal needs both: a mechanism that can make the pattern, and a reason the pattern was kept.

This atlas puts them side by side. Eight patterns, each with the mechanism that builds it in the embryo, the job it does in the wild, and the study the claim rests on. The swatches are drawn in code rather than photographed, so you can see the pattern without the animal, and each one can be borrowed as the coat of a creature in the hybrid animal generator.

“It is suggested that a system of chemical substances, called morphogens, reacting together and diffusing through a tissue, is adequate to account for the main phenomena of morphogenesis.”

Alan Turing, The chemical basis of morphogenesis, 1952

The machinery

How animals get their patterns

Turing's idea needs only two ingredients. One chemical, the activator, makes more of itself and switches pigment on. The other, the inhibitor, is produced by the first, spreads faster, and switches pigment off. Where the activator wins you get a dark patch; around it the inhibitor has spread further than the activator, so the next dark patch can only start some distance away. Repeat across a sheet of skin and the result is a pattern with a wavelength: spots, stripes or a maze, depending on the rates.

For decades it was a mathematical curiosity, because nobody could find the two chemicals. The doubt faded as real cases turned up in fish, in mice and in the ridges on the roof of your mouth, and a 2023 study filled the last obvious gap: real patterns have edges far sharper than the equations produce, because the chemical gradient also carries the pigment cells along with it.

Not every pattern on this page is a Turing pattern. The chipmunk's stripes are drawn by a gene switching pigment cells off in bands; a cow's white patches are places the pigment cells never reached; a deer's pale belly is the far end of their journey. The atlas says which is which.

One mechanism, two outputs. Run the same equations on a wide field and they settle into spots; run them on a narrow one and the spots have no room and merge into bands. That is why a cheetah's body is spotted and its tail is ringed, and why the reverse, a striped body with a spotted tail, does not exist.

The atlas

Eight patterns, each with its maker and its job

Ordered from the most to the least Turing-like. The first four come out of the same reaction-diffusion machinery in different settings; the last four are made other ways. Where a study has tested the function, the card says so; where the function is only the usual reading, it says that instead.

Stripes

Worn by plains zebra, tiger, okapi (legs only)

Made by
A reaction-diffusion system: one chemical signal switches pigment on, a second spreads faster and switches it off nearby, and the two settle into bands. Turing wrote the equations in 1952. The bands they predict have soft edges, and a 2023 study added the missing step: the chemical gradient also drags the pigment cells themselves, which is why a zebra's edge is a line and not a smear.
Used for
On zebras, keeping flies off. Across equid species and subspecies, the amount of striping tracks the range of biting tabanid flies, and on a horse farm in Britain far fewer horseflies landed on zebras than on horses; horses dressed in striped coats got the same protection. On tigers, hiding: to a deer, which sees two colours instead of three, orange in a forest is close to the best camouflage a mammal can grow.
Evidence
Turing 1952; Alessio & Gupta 2023; Caro et al. 2014 and 2019; Fennell et al. 2019.
Plains zebra standing side-on in short grass at Etosha, black and white stripes running down the flank and legs
Plains zebra, Etosha National Park, Namibia. CC BY-SA 3.0 · Yathin S Krishnappa · source

Spots

Worn by cheetah, serval, fawns, ocelot

Made by
The same two signals as stripes, in a different geometry. The mechanism's output depends on the size of the field it runs on when the pattern is laid down: a wide sheet of embryonic skin settles into spots, a narrow one settles into bands. That single rule predicts something you can check on any cheetah: spots on the body, rings on the tail. The mathematician James Murray, who ran the first simulations, pointed out that there are spotted animals with striped tails but no striped animals with spotted tails.
Used for
Breaking an outline against dry grass, where a solid tawny cat would read as a shape. The cheetah's spots also inherit the general property of small marks: they disappear at distance, so a hunting cat is a blur before it is a cat.
Evidence
Kondo & Miura 2010; Murray's tail argument, as set out in The Conversation.

Rosettes

Worn by leopard, jaguar, clouded leopard, and the king cheetah by mutation

Made by
A spot whose centre is filled back in with the ground colour. Cats show how little it takes to move between the types: the gene Taqpep decides whether a domestic tabby wears thin mackerel stripes or broad blotches, and in the cheetah a mutation in the same gene fuses ordinary spots into the blotches and stripes of the king cheetah. One gene, and the pattern changes category.
Used for
Matching dappled light. Across the cat family, the species that live in dense cover, hunt in trees or move at night are the ones most likely to be patterned, and their patterns are more complex and irregular; the leopard's rosettes are the forest case, the lion's plain coat the open-country case.
Evidence
Allen et al. 2011; Kaelin et al. 2012.
African leopard lying along a tree branch with legs hanging down, rosettes visible across the flank and legs against sky and bark
African leopard resting in a tree; the rosettes break the outline against branches and sky. CC BY-SA 4.0 · Sumeet Moghe · source

Patches

also called reticulation, when the lines between them are thin

Worn by giraffe

Made by
Large blocks of pigment separated by a pale network. How the giraffe's embryo lays them down is not settled, but the shapes are inherited: in wild Masai giraffes, the roundness and irregularity of a calf's spots can be predicted from its mother's, which is what you would expect if genes rather than chance set the pattern.
Used for
Hiding the calf. The same study followed the calves and found that those with larger and more irregular or rounder spots were more likely to survive their first months, consistent with the old hypothesis that giraffe markings exist to hide newborns from visually hunting predators.
Evidence
Lee et al. 2018.
Two Masai giraffes standing in green bush at Arusha, their jagged brown patches separated by pale lines
Masai giraffes, Arusha National Park, Tanzania. No two patch layouts are the same. CC BY-SA 4.0 · Charles J. Sharp · source

Dorsal stripes

Worn by chipmunk, African striped mouse, thirteen-lined ground squirrel

Made by
Not a reaction-diffusion pattern at all. In the African striped mouse, a gene called Alx3 is switched on in bands along the embryo's back before any pigment exists; where it is on, it holds back the maturation of pigment cells, and those bands grow pale hairs. Chipmunks use the same gene in the same way, which means two rodents on different continents arrived at stripes by the same route.
Used for
The paper is about how the stripes are built rather than what they are for; the usual reading is concealment among grass stems, where a striped back is a broken line instead of a solid one.
Evidence
Mallarino et al. 2016.
Four-striped grass mouse in dry grass, seen from the side, with dark and pale stripes running the length of its back
Four-striped grass mouse, southern Africa. The stripes are made by a gene switching pigment cells off in bands. CC BY-SA 2.0 · Bernard Dupont · source

Countershading

Worn by deer, sharks, penguins, most fish, most mammals

Made by
The simplest gradient in the atlas. Pigment cells in a mammal embryo start along the spine and spread outward and down, so the belly is the last skin they reach and the first place they run thin. Dark on top, pale underneath, with no pattern-forming chemistry required.
Used for
Cancelling the shadow. Sunlight from above paints an animal darker below, which is how a predator reads it as a solid. Pale undersides fill that shadow in and flatten the body. The painter Abbott Thayer proposed this in 1896; the experiments that showed it works came a century later.
Evidence
Rowland 2009; Mort et al. 2016 on how pigment cells colonise the skin.

Piebald

also called white spotting

Worn by cattle, dogs, cats, horses, and almost nothing in the wild

Made by
Pigment cells that never arrived. The precursors of pigment cells multiply and wander from the back of the embryo across the skin; if there are too few of them, or they divide too slowly, patches of skin are left uncolonised and grow white. A mathematical model calibrated on mouse embryos showed that the white belly spots of Kit-mutant mice come from reduced cell division, not from cells failing to move.
Used for
Mostly nothing. Piebald coats are common in domestic animals and rare in the wild because they were kept by breeders, not by predators: a white-patched animal is easy to see and easy to tell apart, which is exactly what a farmer wants and a fawn does not.
Evidence
Mort et al. 2016.

Warning bands

also called aposematism

Worn by striped skunk, wasps, coral snakes, poison dart frogs

Made by
Developmentally the least interesting pattern on the page: a few large blocks of contrasting colour, laid down early and kept simple, because simplicity is the point.
Used for
Being seen and remembered. A skunk's white stripe and a wasp's bands are signals to predators that the animal is defended, and a predator that has been sprayed or stung once learns the pattern rather than the individual. In a functional survey of visual signals between species, this anti-predator warning is the best-studied category, and it works because the pattern is bold, contrasting and shared across many defended species.
Evidence
Caro & Allen 2017.
Striped skunk on dry grass with its black-and-white tail raised high, the white stripe running from the head down the back
Striped skunk with its tail up. The stripe is aimed at the predator before the spray is. Public domain · Wallace Keck · source

A pattern with an expiry date

Why baby animals have spots their parents lack

Fawns, tapir calves and lion cubs are born patterned and grow plain. The pattern is built for the first weeks, when the animal cannot outrun anything and survives by lying still in dappled shade, and it is worth the cost only for as long as that is true. Once the animal can run or fight, the spots fade, because a spotted adult on open ground is easier to see, not harder.

The giraffe study on the patches card is the cleanest test of the idea so far: calves with certain spot shapes survived their first months more often, and a giraffe keeps its calf pattern for life because a giraffe never stops needing to stand among trees. The tapir calf below takes the other route. Its stripes and dashes match forest-floor light and are gone within a year.

Malayan tapir calf asleep on straw, dark brown with pale stripes and dashes along its body, next to the grey flank of an adult
Malayan tapir calf beside its mother. The adult is black and white in two blocks; the calf is striped for the forest floor. CC BY-SA 3.0 · Sasha Kopf · source

Try it

Borrow a pattern

The generator has a Color / Pattern slot, and these links lock it to one wearer from the atlas and leave every other part to the roll. What comes back is a test of the rule above: the coat stays, the body underneath changes, and you can judge for yourself whether zebra stripes still look fly-proof on a bird.

Zebra stripesFly-proof bands on whatever body turns up.Load →Cheetah spotsSpots on the body, rings on the tail.Load →Leopard rosettesForest light on a creature that never saw a forest.Load →Giraffe patchesBig blocks and pale seams.Load →Chipmunk stripesGene-drawn lines down the back.Load →Skunk warningA creature that wants to be noticed.Load →

Patterns elsewhere on the site

If you are drawing one of these coats onto an invented animal, the hybrid drawing guide has the rule that follows from this page: let the pattern wrap the form, not the part boundaries. The okapi, which wears zebra stripes on its legs and nothing on its body, is taken apart in the guide to real animals that look fake. The camelopard, the giraffe's old English name, is literally a camel wearing a leopard's spots, and the guide to how animals got their names follows that word back to the 1300s. And every wearer in this atlas is in the animal library, photographed in its own coat.

Where this comes from

Sources for these eight patterns

Every mechanism and function on the cards is tied to a named study. Publisher pages for Nature, Science and the Royal Society are linked through their open-access copies where one exists; the two that have none are linked by DOI.