It’s no secret that moths have a bit of a light obsession — whether they’re fluttering around your back porch bulb or cozying up to a street light.
But light pollution from these artificial sources isn’t just a problem when it comes to viewing the heavens. A study published in August in the journal Science Advances has new evidence for why these lights might be causing damage to moth populations as well — impacting their entire ecosystem as a result.
“Moths are functionally important for terrestrial ecosystems, including as pollinators, prey for both vertebrates (e.g., birds and bats) and invertebrates (e.g., spiders and social wasps), and hosts for parasitoids,” write the study’s authors. “These changes are expected to have substantial cascading consequences for ecosystems.”
In this study, the researchers looked at the moth’s least mobile stage: the caterpillar.
What’s new — The team studied moths' overall abundance and size at dark field sites, those lit by LED streetlights, or sites lit by alternative wavelength lights (e.g., high- and low-pressure sodium lamps).
Despite these locations being otherwise identical in terms of plant life, the researchers found close to 50 percent fewer moths in lit areas, with LED lights, in particular, having the fewest.
They also found, perhaps counterintuitively, that the moths they did find at lit sites were much heavier than their darkness-preferring counterparts.
“Caterpillars that were heavier in the lit section at the time of sampling may suggest advanced development under stress and investment in earlier pupation,” write the authors. “This is predicted to have deleterious effects on adult fitness.”
What makes LED lights different — While non-natural light isn’t great for moths across the board, Boyes says that LED light — which emits “white” or full-spectrum light — are some of the worst culprits simply because they cover the widest range.
“The more wavelengths of light that are emitted, the greater the diversity of species and biological processes that are likely to be affected,” Boyes tells Inverse. “The color of white LEDs is also much more similar to daylight than sodium lights, so biological processes that are controlled by daylight are predicted to be more readily disrupted.”
Despite these issues, Boyes says that LED streetlights have become more and more common, especially in the U.K., where Boyes conducted this research.
“[LEDs] save money and carbon emissions as they are more energy-efficient,” he says. “They are more reliable. In the U.K., 55 percent of streetlights are now LEDs, and the rest have almost all been contracted to be replaced.”
But because of something called the rebound effect (the idea that swapping old light sources for energy-efficient lights will create more overall demand for lights), Boyes says the energy and cost savings for LEDs will ultimately be smaller than first thought.
Aren’t moths attracted to light?
But let's rewind: how can artificial light be bad for moths when they willingly fly towards it as adults? In many ways, this is still an open question for scientists.
When it comes to fully grown moths flying toward lightbulbs or fire, scientists’ best guess is that these light sources confuse the otherwise nocturnal insects’ sense of direction. Scientists theorize that moths use the parallel light from the stars and moon to navigate in straight lines but get confused by artificial light sources that radiate in all directions. As a result, they will fly loops around lights instead.
Other researchers have also theorized that moths may be confusing these light sources for either sexual partners or food.
But like many human vices, what might be acceptable in moderation for mature moths appears to be harmful to them when they’re still growing.
And this won’t just be a problem for moths, Boyes and colleagues write in their paper. As crucial species in these grassy ecosystems, a decline in moth or other nocturnal insect species populations will snowball into negative effects for their predators or benefactors as well, including songbirds, bats, and other pollinators.
And if we learned anything from the decline of bees, it’s that threats to pollination will trickle down to humans as well.
How humans can do better — LEDs aren’t the only thing threatening moths and other insects — habitat loss and climate change play a big role too — but Boyes says there’s at least a pretty simple solution to this one problem: to reembrace the night.
“The nice thing about the topic is that there are cheap, easy solutions unlike many other threats to wildlife, which can be much more tricky,” Boyes says. “Importantly, LEDs can be modified much more easily than sodium lamps – at marginal cost - by reducing intensity through dimming and using filters to reduce blue wavelengths of light that are most harmful to insects. We predict this would help.”