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Beetles use their brightly coloured shells as camouflage

Scientists have shown how vibrantly-coloured animals can increase their chances of survival by offering a form of camouflage.

Researchers in Bristol showed how the gleaming, metallic wings of jewel beetles help conceal themselves against plants to hide from predators.

Animals being brightly coloured had previously been thought to have two main purposes – to catch the eye of potential mates or warn predators that they may be poisonous.

While male peacocks display colourful feathers to attract the opposite sex, monarch butterflies use their wings to signal to predators that they carry a toxin.

By comparing how effectively birds catch insects with and without this iridescent green coating, the research team have shown this third benefit – camouflage.

Jewel beetles have iridescence - they appear to change colour slightly when they are viewed from different angles

Jewel beetles have iridescence – they appear to change colour slightly when they are viewed from different angles

‘Our study is the first solid evidence for the idea that iridescence can work as highly-effective form of camouflage, and ultimately this could explain why iridescence has evolved in so many different species of animals,’ said Dr Karin Kjernsmo, an evolutionary and behavioural ecologist at the University of Bristol and first author on the study.

Iridescence – the ability to gradually change colour when viewed from different angles – is common in nature.

‘Iridescence has evolved independently in everything from jewel-like insects to shimmering birds and can even be spotted in your garden in insects such as Rose Chafers and Rosemary beetles,’ said Dr Kjernsmo.

The Bristol team wanted to find out why vivid metallic colours had evolved in so many species of animals, from insects, to birds and reptiles.

They conducted a study using the vivid metallic jewel beetle, Sternocera aequisignata, which is known for its iridescence.

The team placed iridescent and non- iridescent beetles on leaves in the forest and noted their survival against attacks by wild birds.

This images demonstrates jewel beetles' angle-dependent change in colours from three different angles

This images demonstrates jewel beetles’ angle-dependent change in colours from three different angles

Thanks to the bright green exterior of the beetles, they would have been hard to spot among the similarly-coloured branches.

They found that those with iridescence survived best against birds, providing evidence that the metallic green covering can increase survival.

The team also speculated that these bright metallic shells could have evolved in beetles to confuse birds, which are their primary predator.

You won't see me: Beetles blend in well with surrounding plant life, like this one which can just about be located near the bottom-centre of the photo

You won’t see me: Beetles blend in well with surrounding plant life, like this one which can just about be located near the bottom-centre of the photo

‘Although an iridescent insect might be easy to spot in a well-lit museum case, these spectacular colours may not shine as brightly in the dappled light of a natural environment, and so an iridescent beetle on a shiny leaf could be much more difficult to detect,’ said Dr Kjernsmo. 

What if the birds had noticed the iridescent beetles, but were less inclined to eat them due to their distracting colour – possibly perceived as an indicator of poison, like in monarch butterflies?

To test this, the researchers conducted a final experiment in which they asked human participants to search for the beetles in the same environment.

Much like the birds, humans had difficulty spotting the iridescent insects among the leaves. 

Costa's Hummingbird with a stunning iridescent purple throat feathers catching the light

Costa’s Hummingbird with a stunning iridescent purple throat feathers catching the light

According to Dr Kjernsmo, the study is described as the first solid evidence that iridescence can work as a highly-effective form of camouflage.

It may explain why iridescence has evolved in so many different species of animals, from wasps, to snakes to butterflies, peacocks and snakes.

Dr Kjernsmo said this is because iridescence has a ‘masking ability’ that creates the ‘illusion of inconsistent features and depth’ which confuses potential predators. 

The team believe there may be other species in the animal kingdom with iridescent camouflage.

‘We don’t for a minute imagine that the effect is something unique to jewel beetles; indeed, we’d be disappointed if it was,’ Dr Kjernsmo said.

‘If we found that these beetles could be concealed by their colours, it increases the chances that many iridescent species could be using their colours this way.’ 

The findings are published in the journal Current Biology.

 

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