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Nature’s colour coding for poison

Posted in Animals, Insects, Nature, Wildlife on Saturday, 13 February 2016

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This edited article about poisonous creatures originally appeared in Look and Learn issue number 1018 published on 12 September 1981.

ladybird, picture, image, illustration

The colourful but poisonous ladybird is avoided by birds

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.

Moving from above ground to under water, the crested or warty newt, a widespread British amphibian often found in garden ponds, has a bright orange or reddish-orange belly with blackish or dark grey spots and blotches.

Any potential predator would be well advised to heed this warning, for the warts on the crested newt’s back contain poisons. However, this is comparatively mild when compared with that of a newt found in California, which contains the deadly poison tetrodotoxin. A mere .001 grams of this is sufficient to kill 7,000 mice.

North America has far more venomous creatures than we have in Europe. One of the best known is the rattlesnake, which uses an audible warning – its rattle – to protect itself. In contrast, the coral snake lacks such a refinement as a rattle to alert potential predators to stay away, but employs brilliant warning colours instead.

A bite from a coral snake can cause death within 24 hours, and young children are especially vulnerable to the poison. Another North American snake, the king snake, has copied the coral snake’s warning colours, though it is not poisonous. There is a rhyme in the States which tells you how to tell the coral snake from its impostor:

Red on yellow (or white)
Kill a fellow (or might)
Red on black
Venom lack.

In Britain an extraordinary number of people are scared of spiders, though we have none that can do more than tickle you. In the Tropics and warm countries of the world there are certain species which are best avoided, and the widely distributed black widow is one.

As its sinister name implies, this creature can kill a human being, but its black body and legs, with bright red dumb-bell shaped mark on the underside of its abdomen, warn that this is the most dangerous of all the spiders.

South America’s rain forests shelter a great number of frogs which employ vivid warning colours to advertise to the world that they are best left alone. The painted frog of Panama sits wherever it pleases, for no predator will come near its venom-laden skin. Its body is shiny black with brilliant crimson stripes.

Most venomous of the South American frogs is the arrow poison frog, but as its name suggests, carrying such a powerful poison has worked against it, for the native Indians kill it and dip their arrows in its poison. This is called batrachotoxin, and it is the most lethal of all the animal venoms which are known to man. Not surprisingly, South American Indians do not emulate Frenchmen and eat frog legs!

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