Treehoppers’ spectacular headgear is both a ‘Spidey-sense-like’ electrical warning system and a bioelectric cloak

From the ultra-high frequency hearing of the Greater Wax Moth to the polarized light-detecting eyes of mantis shrimp, evolution by natural selection has produced a spectacular array of sensory adaptations that enhance survival. One of the most uncanny sensory adaptations found in nature is electroreception, the ability to detect faint electrical fields.

Though most common among aquatic and semi-aquatic animals, this sensory ability is also found among a handful of insects.

A new study published in the Proceedings of the National Academy of Sciences describes a bizarre insect with previously unrecognized electroreception ability: the treehopper. Setting the treehopper apart from other electroreceptive insects is the way its body went to evolutionary extremes to better harness this ability.

Treehoppers, which are closely related to cicadas and leafhoppers, are most notable for their strikingly massive and otherworldly pronotum, a shield-like segment of thorax located just below the heads. This feature, which extends either forward or backward, depending on the variety of treehopper you encounter, can resemble horns, spikes, parts of plants, and other indescribable shapes.

Among insects, such features can provide excellent camouflage to help deter would-be predators. The pronotum of the treehopper, however, is so incredibly distinctive (some species even stand out with bright colors and bold patterns), that it caught the attention of scientists who theorized there may be more to this feature than meets the eye.

“The function of these morphological extremities and the reasons for their evolution have thus far remained largely enigmatic,” the authors write in the paper.

To explore the potential of an evolutionary form-follows-function reason behind this adaptation, the researchers hypothesized that the treehopper’s massive, complex pronotum may react in the same way that antennae on certain bees, mites, and caterpillars respond to static electric fields.

To test this idea, the researchers first had to quantify the electrostatic charges in the treehopper’s natural habitat, so they measured the charges of various wild treehoppers, wasps, and bees in multiple locations around Costa Rica. The readings were taken as the various insects passed through a ring electrode system.

Their data included a total of 151 individual treehoppers, two species of wasp, and two species of stingless bees. They then calculated the strength and structure of an electric field that would exist between a typical treehopper on a plant and an approaching predatory wasp.

The results showed that there was a detectable electric field when the two were in close proximity. Remarkably, the fields detected around the most protruding portions of the treehopper’s pronotum were 50 times stronger than the baseline readings.

The researchers also found that the bizarre helmet-like morphology of the treehopper’s pronotum decreased its detectability to any electroreceptive predators; nature’s own form of an electrical cloaking device.

“Our study reveals that the extreme morphologies seen in animals such as treehoppers may increase their sensitivity to electrical stimuli,” the authors write, highlighting the remarkable connection between form and function, even when it is inconspicuously connected to such a conspicuous adaptation.

Until the mid-1980s, most scientists thought that electroreception was only found in fishes and amphibians. Then in 1986, researchers confirmed that platypuses could also detect weak electrical fields.

This was also confirmed, but to a lesser degree, among the platypuses’ more terrestrial relative, the echidna. More recently, in 2013, a team of scientists led by Daniel Roberts, a co-author on the new paper, discovered that bees could also detect minute electrical fields produced by flowers.

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