FunNature & AnimalWhy are some insects iridescent?

Why are some insects iridescent?

Shifting metallic glitters have evolved independently in the animal kingdom, from dazzling hummingbirds to skinks, a type of lizard, and jewel-like flies. In some animals, such as peacocks, the iridescence is more prominent in one sex than the other . In these cases, sexual selection has had a lot to do with it.

However, in many insects both sexes are equally iridescent , and some animals are only iridescent in their larval forms, such as bush beetles ( Trirhabda bacharidis ). A new study published in Animal Behavior has provided experimental evidence that color changes may also have a protective function .

“One of the challenges in studying the functions of such a reflective structural coloration has been to separate the effects of color mutability, the hallmark of iridescence, from the effects of simply having multiple colors at the same time,” he explains. the biologist from the University of Bristol who has participated in the research Karin Kjernsmo. “And also to separate the effects of brightness from those of iridescence.”

To achieve this, Kjernsmo and his colleagues launched an experiment in which they tested young chickens with different “prey” in the form of real and artificial jewel beetle ( Sternocera aequisignata ) wing boxes with a tasty morsel of mealworms in them. its interior.

The chicks, who had never encountered this type of prey, were presented with wing boxes that were matte with a static gradient, glossy with a static gradient, matte with changing hues, or glossy with changing hues.

The young birds did not hesitate to attack the “prey” that showed several colors at the same time. But they thought twice before going after the “prey” whose color changed iridescently. The brightness also induced a single dither, but not as strong as the color changes. As the chicks had no previous experience with iridescence, this behavior was clearly instinctive.

“Here we have managed, for the first time, to effectively test each of these two effects separately and have shown that both iridescence and brightness can protect prey even after detection, providing another adaptive explanation for the evolution and existence pervasive iridescence,” says Kjernsmo.

In 2020, the same team provided evidence that iridescence can be an effective form of camouflage , though it may seem counterintuitive given how surprisingly attractive some of the bright structural colors can be.

“This idea is very old, but it’s never been proven. I think it’s just been neglected or forgotten,” Kjernsmo told Discover magazine at the time.

These results would have to be demonstrated under natural conditions and not just in a laboratory setting.

“Our results are important because they demonstrate that even when prey are presented up close and against a mismatched background, iridescence can confer a survival benefit by inducing hesitation or even, as is sometimes observed, an aversion response. in attacking birds,” Kjernsmo and team wrote in their paper.

They explain that this aversion may be due to a form of aposematism , which is when animals use colors to announce to others that they are poisonous. A 2017 study on an iridescent alpine leaf beetle ( Oreina cacaliae ), with known chemical defenses, showed that brightness enhanced its warning signal, supporting the earlier idea.

“Future studies could establish the frequency with which the combination of iridescence and secondary defenses occurs,” suggest the researchers of the current study.



KarinKjernsmo, K et al. 2022. Beetle iridescence induces an avoidance response in naïve avian predators. Animal Behaviour. DOI:

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