Nature’s best visual trick is iridescence, which can transform an ordinary beetle into something extraordinary. The dried up beetle carcass above is one of the prettiest examples of iridescence I’ve ever seen up close. The beetle is a golden buprestid (Buprestis aurulenta) which lives in my biome. As larvae they spend two to four years mining through recently dead conifer trees, whether that tree is rotting on a forest floor or part of your new coffee table, earning themselves the title of ‘pest’.
Once they morph beyond the furniture-eating stage, their exoskeleton matures to an iridescent green with brass coloured fringes around the wings. Strung together, these beetles would make a necklace suitable for a fancy ball, and I’m not the first to consider an iridescent beetle fit for a resplendent occasion. Ellen Terry, perhaps the most famous actress in the Victorian era, wore a green dress decorated with iridescent beetle wings to play Lady MacBeth in 1888. The dress must have looked stunning under the stage lights.
Beetles don’t hold a monopoly on iridescence; in fact, a diverse group of animals have independently evolved with their own version of colours with variable intensity and hue depending on the angle they are viewed (1). Examples abound in my own yard from dragonflies, butterflies to hummingbirds and more.
Why be iridescent?
An obvious use of iridescence is to communicate. A flash of bright colour might scare a predator away or say “I’m poisonous, so don’t eat me”. Or an animal could produce a flashy show to attract a mate (these guys put on the best show, but unfortunately don’t live in my yard). An untested hypothesis is that iridescence may help a school of fish or a flock of birds organize themselves (1) – another form of communication. For example, the iridescent patch on a mallard duck‘s wing may be a cue to help them fly in the same direction.
Counterintuitively, iridescent colours can also be used to hide (1), which explains why little fish like herring and sardines are so shiny – when looked at from below, their shininess blends with the shininess of the ocean surface. Or an animal can use iridescence to pretend to be something else – what looks like a drop of dew on a leaf might actually be a green leaf beetle (golden buprestids are probably to big to do this).
Interestingly, some instances of iridescence evolved before the organisms bearing iridescent structures developed the ability to see (1). One theory as to why iridescence evolved is that the structures that can create iridescence also create strength – so perhaps the iridescence of the golden buprestid is a side-effect of building a strong exoskeleton. We know these exoskeletons last, as fossilized beetles as old as 49 million years have been found that are still iridescent (2).
Now, I’ll need to find about a thousand more golden buprestids to make a ballgown of my own.