Sciences & Technology
New dimensions in colour
A bit of bling helps insects dazzle their predators
Beyond just looking stunning, shininess may help insects confuse predators to avoid being eaten
Published 19 November 2024
Wearing a bright outfit covered in shiny sequins is a sure-fire way to attract attention.
Just think of stars on stage – Beyonce, Taylor Swift or Harry Styles – their bedazzled outfits catch the lights, flashing and sparkling as they dance in concert.
Many animals also have brilliant and dazzling appearances. Jewel beetles look like, well, jewels and there’s even a fly so fabulous it was named after US entertainer Ru Paul - Opaluma rupaul.
If these brilliant appearances attract attention, then why aren’t these animals the first to be eaten by predators?
It turns out that a key characteristic of these appearances – their changeability – may actually help animals to escape predators.
Mirror ball effect
Shiny animals produce bright flashes when they reflect the sun and some very shiny animals also reflect their surrounding environment. As these animals move, flashes are produced and the reflections on the surface of the animal change – similar to a mirror ball.
For a predator, this means it is trying to follow and attack a visually changeable target. A task like this is challenging – studies with both bird and insect predators have shown that attacks are less accurate towards changeable prey.
But what is causing this effect?
Can predators visually track the prey? Do they misjudge prey speed? Are optical illusions involved? Many predictions have been made, but none have been tested until now.
Tracking a moving target
From studies with humans, we know a little bit about how moving shiny or flashing targets may be perceived.
Black and white stripes can disrupt speed perception and make a target look like it is moving faster or slower than it really is. Highly reflective shiny targets may produce a similar effect, causing predators to misjudge prey speed.
Alternatively, optical illusions can impact the localisation of the target. The flash-lag illusion is where a flash appears to slightly trail behind a moving object even though it is really at the same location.
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The bright flashes from a shiny animal may cause a similar effect, causing predators to perceive the prey’s position as slightly behind its real position.
Both disruptions to speed perception and the flash-lag illusion could cause directional errors in predator behaviours.
Or, in other words, predator visual tracking and attacks may more often be ahead of the target (speed disruption) or trail behind the target (speed disruption or flash-lag illusion), relative to the target movement direction.
It is also possible that the changeable appearance of shiny prey makes it more difficult for predators to precisely determine the location of moving prey.
This is different to the flash-lag illusion because the predator could misjudge the prey’s position in any direction.
In this case, predator visual tracking and attacks may be less accurate, but the errors in accuracy are in all directions – ahead of the target, behind the target, too close or too far.
Disrupting perception
We tested these predictions by using a high-speed camera to film jumping spiders attacking fake, moving targets. The targets were either really shiny, matte or matched the background colour of the arena.
Jumping spiders are perfect predators for this experiment because they prefer to attack moving prey, they are known to eat both shiny and matte prey animals, and they have excellent vision. Even better for researchers is that they attack fake moving prey in the lab without much encouragement.
From the high-speed footage, we could quantify how well the jumping spiders visually tracked the different targets and how accurate their attacks were.
It turns out that jumping spiders are worse at tracking and attacking shiny targets than matte targets or those that match the background.
In fact, their tracking was almost two times more variable towards shiny targets and their attacks were the equivalent of two target widths further away from shiny targets.
These results were not directional relative to the target’s path of movement. Therefore, we did not find any support for the idea that shininess disrupts speed perception or that localisation is disrupted by the flash-lag illusion.
Instead, our results show that shininess creates an unpredictable target, hindering a predator’s ability to precisely localise a moving, shiny animal so their attacks miss by greater amounts in any direction. So even though shiny animals can catch the eye, they are difficult to localise and capture.
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Our study provides a first look at how shiny colours may disrupt perception, but there is still more to understand. We do not know exactly how these effects are visually processed or if they are processed in the same way by animals with very different eyes.
There are also a lot of other factors that could impact the perception of shiny animals.
For example, shininess will be enhanced on sunny days compared to cloudy days. And prey characteristics, such as size, shape and movement behaviour, will also influence the shiny appearance.
We can all appreciate how popstars benefit from shininess, but there is still a lot to learn about dazzling, shiny colours and the role they play for animals.