Insect numbers have plummeted at an alarming rate due to a variety of factors, including increased use of pesticides, farming practices that destroy habitat, and industrial pollution. A new study in the journal Biological Conservation adds another major cause to the list: human-created light pollution.
In a meta-analysis, researchers reviewed 229 previous studies that looked at the impact “artificial light at night” has on insect species. About half of the millions of insect species on Earth are nocturnal, meaning artificial light can have a big impact on their nocturnal life cycles, reports Damian Carrington at The Guardian. Currently, artificial light covers about a quarter of the Earth’s surface.
“Artificial light at night is human-caused lighting—ranging from streetlights to gas flares from oil extraction,” co-author Brett Seymoure of Washington University in St. Louis says in a press release. "It can affect insects in pretty much every imaginable part of their lives."
The impacts vary between insect orders. Excess light makes it difficult for some species, like fireflies, that rely on bioluminescent cues to find mates. Some insects use polarized light to find bodies of water where they breed and reflections from outdoor fixtures confuse their sense of direction. For instance, mayflies, which only live and breed for a day, can be confused by light bouncing off asphalt and lay their eggs in the street instead of a lake or stream. A mistake like that can wipe out an entire population over night.
Insects are also attracted to the headlights of moving cars, with an estimate 100 billion meeting their end on the highway in Germany each summer, according to the study. Artificial light also interferes with the way some insects hunt at night.
Then there are the moths and other flying insects drawn to outdoor lights. It’s estimated about one third of the bugs swirling around those lights die by morning, either by being gobbled up by predators or simply from exhaustion.
Add it all up, and light is one of the major causes of mortality for arthropods.
The researchers write in the study:
“We strongly believe artificial light at night – in combination with habitat loss, chemical pollution, invasive species, and climate change – is driving insect declines. We posit here that artificial light at night is another important – but often overlooked – bringer of the insect apocalypse.”
While the other challenges facing insects requires a total overhaul of the agricultural system and billions of dollars in conservation work, Seymoure tells Yessenia Funes at Earther that light pollution is relatively easy to fix. “With some small changes and some upgrades to lighting, we can still have light at night and drastically reduce light resulting in insect declines,” he says.
According to the press release, the best ways to reduce light pollution are to install directional covers on outdoor lights so they only illuminate the areas where they are needed. Making lights motion-activated so they’re only on when people are around is another solution. Seymoure also says people should pay attention to the color of the light bulbs they use in urban settings. Insects are most attracted to blue and white light, though shades of orange, yellow and red also draw them in. For now, he recommends using amber lights near homes. But the best piece of advice is to simply shut off lights at times and in places when they are not necessary.
Not everyone is convinced that light pollution is a threat on the same level of pesticides. “Light pollution could have significant ramifications at the insect population, species or community level,” Nigel Raine, a pollination researcher from Guelph University in Canada, not involved in the study, tells Carrington. “But it might be too soon to say the impacts are as significant as other stressors.”
According to the new paper, however, the full impact of light pollution on insects hasn’t been assessed, mainly because ecologists have a bias toward studies that take place during the day. That’s one reason Seymoure hopes to dig deeper into the impacts of light pollution on individual orders of insects. In particular, he hopes to look into the ways it affects butterflies, which is more likely to spur public concern, he tells Funes.
Stopping insect declines is urgent. Not only do they pollinate crops and countless wild plants, they are also the basis of many food chains. Without the bugs, many forms of agriculture would cease and entire ecosystems would collapse.
“If we lose these insects, you’re also gone,” Seymoure tells Funes. “It’s over.”