How Gentle Air pollution Might Be Harming Bugs

Walk almost any street at night and it is likely to be well lit. This artificial light at night can affect the migration of wild animals as well as the breeding, hunting and sleeping behavior of the animals.New research has shown that night light can also play a role in decreasing insect populations.

“Light pollution may be discussed a lot, but it is only relatively recently that we have begun to understand how harmful it can be to wildlife. A growing number of studies show that it can be harmful in many ways – to plants, birds, bats, insects, etc., ”Douglas Boyes of the UK Center for Ecology & Hydrology (UKCEH), who led the study, told Treehugger.

To study the impact of artificial light on insect populations, Boyes and his colleagues spent three years studying moth caterpillars in southern England.

“We focus on caterpillars because they usually don’t move very far in their lifetime. So if we take samples at any given point in time, we can be sure that we are accurately measuring local effects (while adults are very mobile and can move several kilometers in life). “Explains Boyes.

“Moths are evolutionarily and ecologically very diverse (several thousand species native to Europe), which means that they should be fairly representative of nocturnal insects and are also relatively well studied. This makes them unique in understanding the effects of lighting on nocturnal insects in general. ”

Counting caterpillars

Measurement of caterpillars.
Douglas Boyes

For the study, Boyes spent more than 400 hours on roadsides studying and counting wild caterpillars. In clearly visible clothing, because he often collected data at night, he visited 27 sites with two different groups of caterpillars that were easy to sample.

Each pair of locations consisted of a hedge or a roadside grass verge lit by street lamps and an identical but unlit habitat. The illuminated areas included 14 that were illuminated with high pressure sodium lamps (HPS), 11 with light emitting diodes (LED) and two with older low pressure sodium (LPS) lamps.

To count the insects, Boyes cut hedges in the spring and summer to count flying caterpillars and swept the grass with nets to count those who only come out at night to climb grass to feed.

Most of the 2,478 caterpillars that Boyes counted came from unlit areas.

Artificial lighting reduced the number of caterpillars by about half to a third, the researchers found. Almost all of the lighted areas that had been lit for at least five years had fewer caterpillars.

Boyes weighed the caterpillars and found that they were generally heavier in lighted areas, which the researchers said was due to stress and accelerated development.“This results in smaller adults who are less evolutionarily fit (fewer eggs, etc.),” ​​he says.

In almost all situations, the results with white LED lighting were worse than with conventional yellow sodium lighting. Boyes points out, “This is worrying given the ubiquitous transition to white LED street lighting.”

They also conducted an experiment where they installed temporary LED lighting in rural grass verges that had never been lit before. They found that the nocturnal caterpillars’ feeding behavior was disturbed.

“Our separate experiment showed that white LEDs interfere with the normal behavior of nocturnal caterpillars – possibly because white LEDs are very similar to daylight, so that the caterpillars“ think ”that it is still day,” says Boyes.

The results were published in the journal Science Advances.

The larger insect picture

LED street lights at one of the study locations.
Douglas Boyes

The researchers examined how their study results could be applied to the larger landscape and found that only 1.1% of the land area of ​​the study area is lit directly by street lamps. Suburban areas are often illuminated (15.5%), but only 0.23% of arable land and 0.68% of deciduous forests are illuminated.

“The evidence suggests that lighting is unlikely to be the main cause of the decline in insects, but it can clearly be contributing to it,” says Boyes. “The main drivers are climate change, habitat loss, agricultural intensification and chemical pollution (including pesticides, nitrogen deposition), but we anticipate that lighting will certainly be important in some contexts.”

The areas that are affected by lighting are getting bigger, he emphasizes. Street lights aren’t the only cause of light pollution, but the study results can help raise awareness of the link between artificial light and potential problems with wildlife.

“They emphasize that lighting is a hugely important local influence, but it may be quite overlooked / underestimated. The nice thing about working in this area is that there are workable solutions (compared to climate change, which is a much harder problem to solve), ”says Boyes.

He suggests that LEDs can be more easily modified than sodium lamps by dimming them and using filters to reduce the blue wavelengths most harmful to insects.

“An ‘insect-friendly’ street lamp would have brightness, maybe red in color (or at least a few blue wavelengths), motion sensors or dimming when very few people are around. If possible, the best solution that has been proven to tell us to minimize the damage to insects is to avoid lighting whenever possible – but of course that is easier said than done. ”