Treehoppers, a group of tiny, hump-backed insects found throughout the tropics, may be hiding a shocking secret. Long known for their flamboyant, horn-like body extensions called pronota, these structures were typically thought to serve as camouflage or defense. But a new study suggests they may also help the insects sense electric fields — possibly allowing them to detect predators and friends alike, just by the static charges they carry.
“It introduces a level of sophistication not previously ascribed to the electrostatic sense,” says Sam England, a biophysicist at the Museum für Naturkunde in Berlin and lead author of the study.
In lab and field tests, England and colleagues found that treehoppers, along with bees and predatory wasps they interact with, carry distinct electrical charges. Using a miniature ring electrode, they measured over 150 treehoppers and hundreds of bees and wasps. Predators tended to be negatively charged, while mutualist bees were mostly positive. These differences, the researchers argue, could give treehoppers enough information to tell friend from foe.
To see whether treehoppers respond to electric cues, the team placed individuals of Poppea capricornis on wooden poles and exposed them to a static electric field similar to what a predator might generate. Nearly half of the insects retreated when the field was active, while just 10% backed away under control conditions.
“Treehoppers were significantly more likely to retreat from the electrode when the electric field was on,” the study reports.
Their responses hint at an ability known as aerial electroreception — once thought to exist only in aquatic animals like sharks, but increasingly recognized in insects. Previous work had shown that bees, hoverflies, and even caterpillars can sense electric fields in air, using tiny hairs or antennae that physically deflect in response to charged objects nearby.
Treehoppers, it turns out, are covered in similar structures — and their elaborate pronota may amplify the effect. Using computer models and scanning electron microscopes, the researchers found that sharp spines and crests on the pronotum concentrate electric fields and guide them to these hairs, much like a lightning rod channels electricity.
“In this case, the electric field in the first 0.1 mm around the extreme pronotum increases by two orders of magnitude to over 100 kV/m,” the authors write.
The study also suggests that two types of hairs — “erect-type” and “pit-type” — may each offer specialized benefits. The erect hairs, found at the tips of spines and ridges, respond strongly to fast-changing fields, like those produced by wingbeats. Pit-type hairs, on the other hand, may detect polarity — whether an approaching insect is positively or negatively charged — and are less prone to “blind spots” directly above them.
In laser-based tests, even the preserved hairs on dead treehoppers vibrated when exposed to simulated wingbeat frequencies of predatory wasps.
What’s more, the peculiar shapes of the pronota may not only boost treehoppers’ ability to sense — but also make them harder to detect. The researchers found that while the field close to the pronotum is intensified, it weakens beyond a short distance, potentially giving the treehopper a kind of electrical stealth.
This dual function — acting both as a sensory antenna and a cloaking device — could help explain why treehopper shapes are so bizarre and varied. And it raises the tantalizing possibility that other oddly shaped bugs might be using electroreception too.
“If this is also the case for electroreception,” the team writes, “specialization within the electroreceptive sense could have contributed to the diversification of adaptive radiations, such as that seen in the treehoppers.”
While camouflage and mimicry likely still play a role, the findings suggest that natural selection may have shaped these creatures’ outlandish forms in part to sharpen their sixth sense — one tuned not to sight or sound, but static.
The study has been published in Biophysics and Computational Biology.
