For insects trying to avoid hungry birds, flashy iridescent shells might not seem like the best evolutionary strategy. But in recent years, biologists have shown that iridescence—lustrous shifts in color, depending on the angle of view—can actually camouflage green jewel beetles among sun-dappled leaves. Now a new study published in Animal Behavior suggests iridescence also works another way to protect these insects, even when they step into plain sight: birds appear to have an innate wariness of the color changes themselves.
This is the first time iridescence, as opposed to simple glossiness or bright colors, has been shown to deter predators. “It’s actually the changeability, the very hallmark of iridescence, that is important for this protective function,” says Karin Kjernsmo, a researcher at the University of Bristol in England and the study’s lead author.
To test how birds reacted to iridescent beetles’ varying colors, Kjernsmo and her colleagues set out real Sternocera aequisignata jewel beetle shells, along with three types of artificial shells: one a glossy green, one a matte green and one color-shifting but matte. They baited the shells with mealworms, then offered this buffet to day-old domestic chicks (this was to ensure any reactions were innate, not the product of learned predation tactics).