Although using flashy colors as camouflage may seem counterintuitive, iridescence obstructs the bumblebee’s ability to identify shape, according to a new study published in the journal Scientific Reports.
Iridescence is a taxonomically widespread and striking form of animal coloration which uses regular repeating nanostructures to reflect light at slightly different angles, causing a color-change effect.
It is common in nature, from the dazzling blues of peacock’s feathers, to the gem-like appearance of insects.
The first links between iridescence and camouflage were first made over one hundred years ago by the American naturalist Abbott Thayer, who is often referred to as ‘the father of camouflage.’ He published a famous book on different types of camouflage such as mimicry, shape disruption and dazzle.
However, iridescence has been rather overlooked for the past century, as it is often assumed to be purely for attracting mates and displaying to other individuals.
The new study is the first to show that iridescence indeed has the potential to deceive predators and make them overlook the prey, the same way disruptive camouflage would work to break up the otherwise recognizable outline of a prey.
“The changing colors make the outline of the prey look completely different to the shape the predators are searching for,” said lead author University of Bristol researcher Karin Kjernsmo and co-authors.
To test whether iridescence impair shape recognition, the scientists used buff-tailed bumblebees (Bombus terrestris) as a model for predatory insect vision and cognition and artificial flower targets with sugar water as prey.
“When presented with different types of artificial flower targets, the bees learned to recognize which shapes contained the sweet reward,” the researchers explained.
“However, they found it much more difficult to discriminate between flower shape when the targets were iridescent.”
The team concluded that iridescence produces visual signals which can confuse potential predators, and this may explain its widespread occurrence in nature.
“It’s the first solid evidence we have that this type of coloration can be used in this way,” Dr. Kjernsmo said.
“Thus, if you are a visual predator searching for the specific shape of a beetle (or other prey animal), iridescence makes it difficult for predators to identify them as something edible.”
“This study has wider implications for how we understand animal vision and camouflage — now when we see these shiny beetles we can know that their amazing colors have many more functions than previously thought.”
“We are currently studying this effect using other visual predators, such as birds as well,” she added.
“This because birds are likely to be the most important predators of iridescent insects.”
Karin Kjernsmo et al. 2018. Iridescence impairs object recognition in bumblebees. Scientific Reports 8, article number: 8095; doi: 10.1038/s41598-018-26571-6