Light pollution could kill essential insect species

It’s no secret that moths are a bit obsessed with light, whether they hover around your back porch light bulb or cuddle up against a street lamp.

But light pollution from these man-made sources is not just a problem when it comes to observing the sky. A study published in August in the journal Scientists progress has new evidence as to why these lights could also cause damage to moth populations, impacting their entire ecosystem.

“Mites are functionally important to terrestrial ecosystems, including as pollinators, prey for vertebrates (eg birds and bats) and invertebrates (eg spiders and social wasps) and hosts for parasitoids, ”write the study authors. “These changes should have substantial cascading consequences for ecosystems.

In this study, the researchers looked at the least mobile stage of the butterfly: the caterpillar.

The populations of red-shouldered thorns (Ennomos alniaria) have fallen by two-thirds over the past 50 years.Iain Leach / Butterfly conservation

What’s up – The team studied the overall abundance and size of moths at dark field sites, those illuminated by LED street lights, or sites illuminated by lights of alternating wavelengths (e.g., sodium lamps at high and low pressure).

On TwitterStudy lead author Douglas Boyes says he alone spent more than 400 hours in different seasons collecting the data.

While these locations are otherwise identical in terms of plant life, the researchers found nearly 50% fewer moths in the lighted areas, with LED lights, in particular, having the least.

They also discovered, perhaps counter-intuitively, that the moths they found at lighted sites were much heavier than their dark-preferring counterparts.

“Caterpillars that were heavier in the lighted section at the time of sampling may suggest advanced development under stress and an investment in earlier pupation,” the authors write. “It should have deleterious effects on the fitness of adults. “

What makes LED lights different – While unnatural light isn’t ideal for moths at all levels, Boyes says LED light – which emits a “white” or full spectrum light – is one of the worst culprits simply because it covers up. the widest range.

“The longer the wavelengths of light are emitted, the greater the diversity of species and biological processes that may be affected,” Boyes explains. Reverse. “The color of white LEDs is also much more similar to daylight than sodium lamps, so biological processes controlled by daylight should be more easily disrupted. “

All over the world, but particularly in the UK, hard white LED lights are increasingly becoming the standard in street lighting.Douglas boyes

Despite these issues, Boyes says LED street lights have become more and more common, especially in the UK, where Boyes conducted this research.

“[LEDs] save money and carbon emissions because they are more energy efficient, ”he says. “They are more reliable. In the UK, 55% of streetlights are now LED, and the rest have almost all been replaced by contract.

But because of what’s known as the rebound effect (the idea that swapping out old light sources for energy-efficient lights will create greater overall demand for lights), Boyes says the energy savings and costs for LEDs will ultimately be lower than initially thought.

Are butterflies not attracted to light?

But let’s take a step back: how can artificial light be bad for moths when they voluntarily fly towards it as adults? In many ways, this is still an open question for scientists.

When it comes to adult moths flying towards light bulbs or fire, scientists’ best guess is that these light sources disrupt the sense of direction of otherwise nocturnal insects. Scientists believe that moths use parallel light from the stars and the moon to navigate in a straight line, but are confused by the artificial light sources that radiate in all directions. As a result, they will loop around the lights instead.

Other researchers have also speculated that moths can confuse these light sources with sexual partners or food.

But like many human vices, what might be acceptable in moderation for mature butterflies appears to be harmful to them while they are still growing.

And that won’t just be a problem for moths, write Boyes and his colleagues in their journal. As a crucial species in these grassy ecosystems, a decline in populations of moths or other nocturnal insect species will also result in negative effects for their predators or benefactors, including songbirds, bats and other pollinators.

And if we’ve learned anything from the decline of bees, it’s that threats to pollination will trickle down to humans as well.

Orange-colored sodium lamps could be a good alternative to LEDs, scientists have found.picture alliance / picture alliance / Getty Images

How humans can do better – LEDs aren’t the only thing threatening moths and other insects – habitat loss and climate change also play a big role – but Boyes says there is at least a fairly simple solution to this problem: remembering it. the night.

“The cool thing about it is that there are some easy and inexpensive fixes out there, unlike many other threats to wildlife, which can be much trickier,” Boyes explains. “It is important to note that LEDs can be changed much more easily than sodium lamps – at marginal cost – by reducing the intensity through dimming and using filters to reduce the blue wavelengths of the light. most harmful light for insects. We anticipate this would help.