Jewel Bug Aggregation

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After following an inch-thick trail of ants for eight meters I stumbled upon a shiny ornament dangling in the dry forest. I was thrilled to find an aggregation of jewel bugs (Scutelleridae: Calliphara nobilis), and it was fascinating to rotate around them and watch the chrome coloration change depending on the angle of incidence. The bugs were iridescent and each had its own distinct set of markings and hue of the metallic shimmer. I removed one from the leaf to smell its characteristic “stink bug” odor*, and as soon as I delicately placed it back on the leaf they all scattered synchronously. This behavior leads me to think that the released chemical may function as an alarm pheromone in addition to a predator deterrent. Some aggregations  of insects scatter readily when disturbed by movement, but the dispersal seemed incredibly coordinated and in sync.

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So the questions goes: why be so conspicuous, and is this aposematic? Usually insects rely on cryptic colorations and camouflage to circumvent detection by predators while others stand out to be seen by predators and actively avoided by harboring distasteful compounds. Well, perhaps jewel bugs are actually tasty prey items… and perhaps they are actually being cryptic to a certain visual system! A study on harlequin bugs (Scutelleridae: Tectocoris diopthalmus) in Queensland revealed that not only did their aposematic coloration deter bird predators, but their deep orange color could not be distinguished from a leafy green background by predatory mantids. Mantids have just a single cone, making them monochromatic with a peak sensitivity ~500-600nm, in “green” wavelengths. They sacrifice acute color perception for heightened spatial recognition for picking out the fine-scale movements of insect prey. It’s easy to fall into the trap of assuming an animal sees how a human does, and it’s important to keep in mind what visual systems are involved when asking questions about animal behavior and perception. Read more about the study here. The diversity of visual systems in the animal kingdom can lead to fascinating solutions in both antipredator mechanisms and conspecific signalling.

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Tropical mantid (Hierodula sp.) from the Top End, Australia; photographed after capture [5]

Most people may seem to think that “stink bugs” have an unpleasant odor, but it is actually pretty nice. It’s a powerful and distinct chemical odor to broadcast unpalability, but I’ve always been puzzled by people’s reactions to it.

Jewel bugs photographed in situ [1] on Rinca Island, Lesser Sundas, Indonesia

Unfortunately I didn’t film the scattering, but here is footage of the jewel bugs
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