This edited article about poisonous creatures originally appeared in Look and Learn issue number 1018 published on 12 September 1981.
Green, amber, red . . . we are all familiar with traffic lights, and understand that green is safe, amber a warning, and red emphatically means “Stop!” Traffic lights are a relatively recent invention, but warning colours are far from new, and have evolved over millions of years. In nature, vivid colours – particularly red – often warn of danger, and it can be as wise to stop well away from an animal or insect with bright warning colours as it is to obey the red traffic light.
In Britain there are few dangerous or poisonous creatures, but if you think carefully you might well recall some examples. The wasp’s bright yellow and black stripes warn of its nasty sting, just as the zig-zag pattern on the back of an adder hints at its venom. In contrast, the harmless grass snake is green. However, have you ever wondered why ladybirds are red and black, or why certain moths, such as the garden tiger and red underwing, have bright red underwings?
The answer, of course, is simple. Ladybirds are poisonous, and their colouring warns birds to leave them well alone. Starlings feed their young on insects, but in a study in Holland it was found that out of 16,484 insects taken to feed nestling starlings by their parents, only two were ladybirds, so their coloration really does protect them.
An interesting aspect of the ladybird’s defence is its ability to ooze blood from its leg joints when attacked. This is called reflex bleeding.
Ladybirds are not the only British beetles to display warning colours, for the cardinal beetle does so too. This crimson-red beetle receives its name from the similarity of its colouring to a cardinal’s robe; like the ladybird, it is also distasteful to birds.
Most moths, when at rest, have cryptic colouring which helps them merge with their background. However, certain species, when disturbed, suddenly reveal bright red underwings, which has the effect of alarming a predator.
This display is called flash coloration, and is often found among grasshoppers, cicadas, moths and butterflies. One of the best examples is the garden tiger, which is a common moth in Britain and often flies by day, even in bright sunshine. Glands in the tiger moth’s thorax secrete a poison, and birds soon learn to avoid this species.
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