Warning colours (aposematism) describes colouration and other markings that send a signal to predators to keep away, often because the owner is poisonous or simply tastes bad. Warning colours are usually two contrasting ones, such as yellow and black, in stripes or blobs for maximum impact to multiple species, since even colour-blind animals can see patterns. As this anti-predation strategy is so useful, some animals cheat. Eye spot patterns make them look like larger organisms or bright colours might warn away even though they are safe to eat. The hoverfly is striped like a wasp, but has no sting.

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