In July 2019, scientists watched mayflies mistake solar-like glass for water; females landed and deposited eggs on the dry surface

Imagine this scenario: it's a summer night in the Hungarian countryside, and thousands of female mayflies gather around the creek, doing one thing that their brief, day-or-two existence as adults is built around: searching for water in which to lay their eggs. The trouble is, many of them never reach the water. Instead, they mistakenly rest on a smooth and black glass panel set up on the side of the creek, lay their eggs on it, then fly away, leaving their offspring to bake and die dry.

This scenario was actually described in a 2020 scientific study titled “Bioreplicated coatings for photovoltaic solar panels nearly eliminate light pollution that harms polarotactic insects,” by Fritz et al., published in the journal PLOS ONE. In July 2019, researchers near Dömörkapu, Hungary, set up several solar panels by the bridge over Bükkös Creek to test which surfaces would fool local mayflies, Ephemera danica, into treating them as water. The explanation for that is rather simple: light, polarized light.

Why a mayfly can't tell a solar panel from a river


The reflection of light off water is unique in the sense that it occurs through horizontally polarized light, which certain groups of insects such as the mayfly, the dragonfly, the caddisfly, and the horse fly have adapted to seek to find a breeding ground. It is a clever strategy that served them well throughout the millions of years it was used before man came along and started covering the planet with dark reflective glass and plastic surfaces, which reflect light just like water.

As pointed out by Horváth, Kriska, Malik and Robertson in their 2009 paper “Polarized light pollution: a new kind of ecological photopollution,” in Frontiers in Ecology and the Environment, there is a technical term for that in ecology known as polarized light pollution, which can talk about not only asphalt roads and dark car hoods, but even grave stones and the glass surfaces of solar panels.

The phenomenon is not a recent discovery by any means. Mayflies were observed laying their eggs en masse on dry roads in the 1960s, according to Kriska, Horváth and Andrikovics in a 1998 article titled “Why Do Mayflies Lay Their Eggs En Masse on Dry Asphalt Roads? Water-Imitating Polarized Light Reflected From Asphalt Attracts Ephemeroptera,” published in the Journal of Experimental Biology. The first observation of that "ecological trap" involved swarms of Hungarian mayflies laying eggs on asphalt roads, mistaking them for water and losing their only reproductive window of the year on a surface where no eggs could hatch.

Why should this matter?

Good question. But replace “creek in Hungary” with “reservoir in Nevada” or “edge of wetlands at a Texas solar plant,” and you’ll find that the physics is the same: polarized light regardless of which nation’s insects see it. Utility-scale solar plants have been rapidly expanding in the U.S. for some time now, and much of the solar panel installation occurs close to exactly the habitat that aquatic insects need to thrive. Aquatic insects that most folks don't even realize exist, such as mayflies, caddisflies, dragonflies, and so forth, serve as important indicator species for the health of freshwater ecosystems, and their presence (or disappearance) can signal broader environmental changes.

The actual twist: a rose petal might fix this

The Fritz et al. group weren't simply counting up the destruction; they were also testing a solution. They took the bumpy, microscopic texture of a rose petal and recreated it into a polymer coating. This was compared to a completely smooth glass-covered surface and a black plastic surface.

The difference was clear: The mayflies hardly ever touched down on the textured "rose petal" surface, but the completely smooth glass-covered and plastic surfaces continued to be touched down on for landing and egg laying, just like the earlier asphalt experiments predicted. The texture interfered with the reflection of light enough to not be interpreted by the insect’s eye as “water,” while still gathering sunlight effectively.

The bigger point

This did not require solar energy to be banned or the shift toward renewable sources to be hindered; it only required a different surface design. This serves as proof that many instances of environmental destruction are not a result of ill intentions on the part of those involved but rather are simply unintended consequences. As solar energy continues to expand throughout the United States, this is the type of behind-the-scenes science that may determine its price.