Street lamps are hurting pollination by distracting insects


Street lamps could be harming agriculture, according to a new study that looks at the effects of nighttime light pollution on pollinators.

Pollinators are animals that fertilize plants by bringing pollen from one to another. The number of pollinators has been going down worldwide, but most research has focused on daytime pollinators like bees. There’s been very little published about nighttime pollinators, like certain moths and beetles, until now. For a study published today in Nature Ecology, scientists set up street lamps in seven meadows that had never been subjected to artificial light before. These meadows, compared to the seven control meadows without the lamps, had fewer visits by pollinators, and the plants produced less fruit.

The amount of artificial light at night is growing by about 6 percent per year, and it has a definite effect on animals, says study co-author Eva Knop, an ecologist at the University of Bern in Switzerland. Many nocturnal animals have very sensitive eyes, so they can be blinded and disoriented. Others may be attracted to the light and then distracted from their natural habitats. Or they may fly away from the lamp. “Insects are at the center of many food webs, so if you disturb them, there’s an effect on the entire ecosystem,” says Franz Hölker, a biologist at Germany’s Leibniz Institute of Freshwater Ecology and Inland Fisheries, who was not involved in the study.

Insects attracted to an LED street lamp.
Photo by Lukas D. Schuler / Dark-Sky Switzerland and xirrus GmbH / Zurich, Switzerland


Knop’s team found 14 different meadows in Switzerland. In seven of them, they set up street lamps that used a type of LED light that is now common in Europe. These automatically switched on at twilight.

First, they wanted to see how the light affected whether pollinators visited the meadows. So the scientists walked around a specific area in the meadows using a hand net to collect all insects touching the flowers. They counted and recorded how many of these pollinators were in each sample. After doing this several times on all the meadows, in both day and night, they found that the meadows with the lights had 62 percent fewer pollinators visiting at night.

This actually does translate into negative effects. The scientists also monitored cabbage thistles and found that the plants in the illuminated meadows produced 13 percent less fruit. “These plants were visited frequently by pollinators during the day, too,” says Knop, “so this means that in the daytime, pollinators simply can’t compensate for the lost pollination at night.”

One limitation of the study is that it only looked at one kind of habitat: meadows. The researchers also haven’t found the exact level at which light pollution becomes harmful, so they want to figure that out in the future, Knop says.

Lights are important for safety, but there are ways to limit the damage. One suggestion, says Knop, is to avoid using LED lights. These have a high percentage of a certain type of light that is particularly harmful to insects. Another option is to use motion-sensing lights that only switch on when someone is nearby. And there’s also light for decoration, which is easier to do without, says Knop. It’ll be for the good of the planet.




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