Light Pollution Linked to Nearly 50% Decline in Insect Populations

Nighttime in Primrose Hill park, London, England.

Nighttime in Primrose Hill park, London, England. stockinasia / iStock / Getty Images Plus

Scientists have grown increasingly alarmed about the decline in insect populations worldwide. While some causes — like pesticide use, habitat loss and the climate crisis — are clear, other potential factors, like artificial light at night (ALAN), are more nebulous.

Now, researchers writing in Science Advances Wednesday told BBC News they have found the strongest evidence yet that nighttime lights really are leading to the decline of local insect populations. In some of the areas they studied, the presence of light decreased moth caterpillar populations by nearly 50 percent.

“We were really quite taken aback by just how stark it was,” lead study author Douglas Boyes from UK Centre for Ecology and Hydrology told AFP.

Previous studies have shown that ALAN can have numerous negative impacts on insects, including increasing their risk of being eaten by predators and disrupting their reproduction and pollination, the study authors noted.

“Yet,” they continued, “it remains unclear whether the effects of ALAN are predominately disruptive impacts on the behavior of individuals or whether ALAN is actively diminishing the populations of pollinators and insect populations more broadly.”

To answer this question the researchers looked at moth caterpillars near roadsides in southern England. They compared the populations of caterpillars at hedgerows and grass margins at 26 sites along lit and unlit roads, BBC News explained. What they found is that there were 47 percent fewer caterpillars in the lit hedgerows and 33 percent fewer caterpillars in the lit grass margins.

In a separate experiment, they also set up lights on fields and found that there were fewer caterpillars under LED lights, suggesting the lights were disrupting feeding.

“In a local setting we can now be quite confident that light pollution is important, but what’s less clear is if we’re looking at a whole landscape,” Boyes told BBC News.

One important aspect of the study is that the caterpillars were more impacted by LED lights than high-pressure sodium (HPS) lamps or older low-pressure sodium (LPS) lamps that create a yellow-orange light, AFP reported. This is troubling because LED lights have grown more popular in recent years because they are more energy efficient.

However, Boyes told AFP that “there are really quite accessible solutions” to the problem.

These include putting filters on the lights to change their color to one less like sunlight, or adding shields around the lights so they illuminate the road and not surrounding insect habitat.

“If insects are in trouble — as we believe they are, and have evidence to support that — perhaps we should be doing all we can to reduce these negative influences,” he told BBC News.

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