The animal world is incredibly colourful, and behind this colour palette is a constant game of survival.
Most animals use camouflage, covering themselves in stealthy patterns to hide from predators. Others display bright and bold colours to warn potential predators they are not a good meal. This second strategy is known as aposematism or warning colouration. Although less common than camouflage, it has evolved hundreds of times in butterflies, beetles, bugs, sea slugs, poison frogs and even birds.
One long-standing question is why species use one of these strategies over the other. Is one of these strategies usually more successful? Under which specific circumstances does one strategy beat the other? Our new study, published today in Science, helps answer these questions.
The hawk moth (Psilogramma casuarinae) has extraordinary camouflage.
Damien Esquerre
Testing multiple theories
Both camouflage and aposematism can co-exist in the same region. In Australia, for example, there are many examples of camouflaged insects such as the spotted predatory katydids and the lichen spiders.
On the other hand, species such as the cotton harlequin bug – a common stink bug found in urban areas – and the handmaiden moth display bright orange and red colours to advertise to predators they are not a pleasant meal. Some animals (but fewer) such as mountain katydids even use both strategies by changing colour, or hiding and revealing colourful patches.
The Australian lichen spider (Pandercetes gracilis) hiding on a skinny tree trunk.
Kate Umbers
There are dozens of theories about why some species are camouflaged instead of warningly coloured, and it is a challenge to pull these ideas apart.
Small localised studies have independently tried to test the effect of different factors separately. For example, we know light levels are important in the success of camouflage strategies. We also know the success of warning colouration often relies on predators having experienced the prey before, and having learned to avoid warning signals.
But is lighting or predator learning ability more important?
Results from a single place tell us about that place, but we see the same strategies all over the world. Do strategies perform the same way everywhere?
To solve this mystery, our large team of collaborators ran the same experiment in 16 different countries around the world, in different forests with different levels of light, and different prey and predator communities.
Cotton harlequin bugs (Tectochoris diophthalmus) display bright orange and red colours to advertise to their predators that they are not a pleasant meal.
Thomas Wallenius
15,000 paper moths
Together we deployed more than 15,000 artificial prey – paper moths – with three different colours: a classic warning pattern of orange-and-black, a sneaky brown that blends in, and an uncommon bright blue-and-black. Each paper target was baited with a mealworm, which allowed us to measure the survival of each type of colouration.