Buzz
Wikimedia Commons // CC BY 2.0
The Hibiscus Harlequin Bug (Tectocoris diophthalmus) faces a unique challenge: evading two distinct predators with opposing defensive needs. However, this clever insect has evolved a stunning solution, utilizing its dazzling shell to serve dual purposes in ways invisible to the human eye.
Birds, one of the bug's predators, quickly learn to avoid it after a few unpleasant encounters. The harlequin bug, related to stinkbugs, contains chemicals that birds find repulsive. After tasting one or two, birds steer clear. However, mantises, another predator, remain undeterred by the bug's taste and consume them without hesitation.
To ward off birds, the harlequin bug employs aposematism, using bright colors as a warning signal. This strategy is common in nature, such as the vivid hues of poison dart frogs. Yet, since mantises are unaffected by the bug's taste, the harlequin must also rely on camouflage to avoid detection. This dual strategy allows the bug to be both conspicuous to birds and hidden from mantises, a delicate balance essential for survival.
How does it achieve this? The answer lies in perception—what stands out or blends in depends on the observer. The harlequin bug's appearance can either make it noticeable or invisible, depending on the predator's visual system and how it processes colors and patterns.
The harlequin bug's secret weapon is its orange hue. Its shell ranges from pale to vibrant orange, often adorned with iridescent blue-green spots. To birds, which possess excellent color vision, an orange bug on a green leaf is highly visible, and the speckles enhance its prominence. However, to mantises, which have poor color vision and see the world in muted tones, the orange bug blends seamlessly into the green foliage. Mantises rely on movement and contrast rather than color, making the stationary orange bug nearly invisible to them.
By wearing the perfect shade, the harlequin bug effectively communicates its unpalatability to birds while remaining hidden from mantises, achieving a dual-purpose defense strategy.
Australian biologists Scott A. Fabricant and Marie E. Herberstein discovered this by simulating how mantises perceive plain orange and spotted harlequin bugs. Their model revealed that orange bugs were nearly indistinguishable from the background, while spotted bugs were slightly more detectable. In experiments, mantises could spot speckled bugs from about a foot away but only noticed plain orange bugs at close range. When given a choice between a plain bug and a spotted one, mantises preferred the latter, but they often ignored plain orange bugs altogether, as if they weren't there.
While orange effectively conceals the harlequin bug from mantises, its shiny spots can still betray its presence. This imperfection in its camouflage may explain the bug's varied appearance across Australia. In regions dominated by mantises, the bugs tend to be pale orange with minimal spotting. In areas where birds are the primary threat, they display brighter shells with more prominent spots. In overlapping predator zones, a balance of spotting and the right orange shade allows the bug to both warn birds and evade mantises.
