Rainbow coloring is not uncommon in nature. It is possessed by both birds and beetles, which have a lot of natural enemies. It was believed that a bright color is necessary for reproduction, despite the fact that it attracts predators. But the new data turned out to be unexpected - this is camouflage.
Asiatic beetles (Sternocera aequisignata) are distinguished by shiny, iridescent exoskeletons that shimmer with all colors. Both males and females have such bright chitin, which indicates the importance of coloration not only for mating.
To find out if the rainbow shell affects the invisibility of beetles to hungry birds, a group of researchers led by ecologist Karin Kjernsmo of the University of Bristol in England conducted an interesting experiment. They attached artificial rainbow beetle shells stuffed with mealworms to leaves in a wild forest, painting the imitations in different colors: blue, green, purple, rainbow, and black. All 886 targets were installed, both bright and inconspicuous.
Two days later, the researchers returned to the forest and counted the "losses". It turned out that the iridescent "beetles" survived the most: the birds ate 85% of the purple and blue dummies and less than 60% of the iridescent ones.
It is unclear whether the birds are experiencing vision problems or are simply afraid of the bright color, warning of the poisonousness of the target. Kjernsmo suggests that rapidly changing colors can disrupt normal bird imaging processes.
As for the people, their results were worse. In the second experiment, 36 people, trying to see in the foliage rainbow and faded dummies of beetles, found less than 80% of blue and purple and only 17% of rainbow ones. That is, iridescence is a wonderful camouflage.