A warning, not a decoration
Why Are Ladybirds Red?
A ladybird is bright red on purpose. It is telling birds that eating it is a mistake they will remember.
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Step 1 of 5
Hiding is one strategy; the opposite is another.
Most small insects survive by being invisible. A ladybird does the reverse — it is slow, obvious and easy to catch, and that only works if catching it is unpleasant.
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Step 2 of 5
It leaks something foul from its knees.
Threatened, a ladybird oozes a yellow bitter fluid from its leg joints. A bird that gets a mouthful spits it out, and does not forget the colour that came with it.
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Step 3 of 5
The warning only works if it is obvious.
A bird has to learn the lesson once and apply it forever, which means every ladybird must look the same and look nothing like food. Bright red on black does both.
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Step 4 of 5
Other insects copy the look.
Some harmless beetles have evolved the same red-and-black without any of the nasty chemistry. They get the protection for free, as long as they stay rarer than the real thing.
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Step 5 of 5
Two pairs of wings, one folded away.
The spotted red covers are hardened front wings. They flip up out of the way and the real flying wings, folded underneath, unfold to more than twice the length.
The number of spots does not tell you the ladybird's age. It tells you the species — and some species have no spots at all.
The short version
A ladybird is bright red to warn birds that it tastes foul, and the warning works because every one of them looks the same.
Try it yourself
Look at road signs for danger. Red, yellow and black, over and over — we use warning colours for the same reason.