How Iridescence Can Camouflage

by Angela Hu

A jewel beetle with a shiny, colourful, and bright shell is perched on a leaf. You assume the colouration is to warn predators or attract mates. But what if I told you that the iridescent shells of beetles are actually to help them hide?

A jewel beetle’s colour is created by tiny structures that diffract the light that falls on them. An interference pattern is generated, resulting in the hues you see. If the iridescence of the beetle was to attract mates, only one of the sexes would be brightly coloured. For the beetle colouration to be a warning, the beetle would be toxic to consume or dangerous. However, the jewel beetle is neither of these. Since it doesn’t mimic any similar organism that has these properties, Dr. Kjernsmo wondered if it could be for camouflage.

Experiment 1

To test out this idea, Dr. Kjernsmo and her colleagues began by building dummy beetles using moulds of shed exoskeletons. They painted them in a number of colours, and also made some by gluing exoskeletons of real beetles onto the dummies. Next, they pinned the dummies to dead mealworms. These were attached to plants growing in a nature reserve and monitored 2, 24, and 48 hours later. If the mealworm was eaten, the beetle was probably attacked by a bird.

Of 886 beetles, 646 were found to be attacked by birds. However, iridescent and black dummies took longer to be discovered by the birds. The iridescent dummies were more than twice as likely to survive compared to the non-iridescent ones. The results of this experiment inspired Dr. Kjernsmo to run a second experiment, this time involving people.

Experiment 2

In her second experiment, she distributed beetle dummies into the woods and asked 36 volunteers to find them. Each had a laser rangefinder that they would point as soon as they saw a dummy. This would show the researchers whether a model was spotted and how close the hunter was.

The results were promising. About 17% of the dummy beetles were found, while almost 80% of the duller coloured beetles were found! When the beetles were on glossy leaves like holly and ivy, they were harder to spot.

For the Future…

More testing is to be done, but it could be that the iridescence confuses predators with an illusion of depth. The hue is so dazzling that it confuses the birds, who can’t see the beetles from the rich colours of the forest. Could other iridescent species also be using their colours to hide? The next step is to involve machine learning. It can “evolve” the colours that will best camouflage an organism in an environment, and match it to the colours of real animals. Ultimately, I think this is an exciting discovery that could change the way we think of animal coloration and camouflage. What other animals use camouflage? Perhaps only time will tell.