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A guided journey · 4 stops

Warning, and borrowing a warning

A warning colour is not a property of the animal wearing it. It is a fact about what predators have learned — which is exactly why it can be stolen.

The route

  1. Warning coloration
  2. Poison frogs
  3. Mimicry
  4. Eyespots

A defended animal gains nothing from killing the predator that eats it. The defence only pays if the predator declines beforehand — so the signal exists to be recognised, and its properties are set by predator psychology rather than by anything about the prey.

Every strange feature of this system follows from how animals learn. Conspicuous patterns are learned faster and remembered longer. Predators generalise, lumping similar appearances together. And because they generalise, a signal can be borrowed by something carrying no defence at all.

This route runs from the signal, to where the defence actually comes from, to what happens when the whole thing is faked.

  1. Stop 1 of 4. Senses and abilities

    Start with the signal, and who has to learn it

    The founding demonstration is worth meeting early: birds that had eaten an unpalatable model afterwards refused a harmless look-alike on sight, and birds without that experience ate it. Same butterfly, opposite outcome, and the only difference was what the bird had previously eaten. Everything else on this route depends on that dependency.

    Read Warning colorationA warning colour only works on an animal that has already learned what it means. Against a predator that has learned nothing, being bright is just being easy to find.

  2. Stop 2 of 4. Reptiles and amphibians

    Find out where the defence actually comes from

    Having established that the signal advertises a defence, the obvious question is what the defence is — and the answer reorganises the animal. Poison frogs do not make their alkaloids. They take them from mites and ants, so a captive frog is not poisonous and wild populations differ with their prey. The defence is a property of a food web rather than of a species.

    Read Poison frogsThe poison is not theirs. They take it from mites and ants — which is why a frog bred in captivity is not poisonous at all.

  3. Stop 3 of 4. Ecology

    Then watch the signal get borrowed

    Because protection lives in what the predator has learned, an animal carrying no defence can benefit from resembling one that does. This is also where the receiver decides how good a copy needs to be: predators generalise broadly, so imperfect mimics are protected, which answers the standing objection that many mimics are not very convincing likenesses.

    Read MimicryA stick insect is not mimicking a stick. Nothing is fooled into treating it as one.

  4. Stop 4 of 4. Insects

    End where the resemblance turned out not to matter

    Eyespots are the case that looks like mimicry and is not. The display genuinely deters birds — butterflies with spots painted out were attacked far more — but when conspicuousness and eye-likeness were varied independently, equally conspicuous bars and squares worked just as well. Ending here returns the route to its own principle: what matters is what the receiver responds to, and nobody had asked until 2008.

    Read EyespotsThe spots do work — birds really do leave the butterfly alone. They just do not seem to work by looking like an owl.

Where this leaves you

You end able to say why "bright colours mean poisonous" fails in both directions, and why the word "bright" was doing unexamined work all along — conspicuous means conspicuous to a particular visual system, and many birds see ultraviolet that we do not.

You also end with the honest state of the subject. How aposematism ever gets started is unresolved: a rare conspicuous mutant among cryptic relatives is easier to find, no predator has learned anything about it, and its defence only helps after it has been attacked.

What the route does not settle: how these signals stay honest over evolutionary time, given that a mimic gets the benefit without paying for the defence.

Last reviewed 2026-09-03. All guided journeys