Streetlights—particularly those that use white light-emitting diodes (LEDs)—not only disrupt insect behavior but are also a culprit behind their declining numbers, a new study carried out in southern England showed Wednesday.
Artificial lights at night had been identified as a possible factor behind falling insect populations around the world, but the topic had been under-researched.
To address the question, scientists compared 26 roadside sites consisting of either hedgerows or grass verges that were lit by streetlights, against an equal number of nearly identical sites that were unlit.
They also examined a site with one unlit and two lit sections, all of which were similar in their vegetation.
The team chose moth caterpillars as a proxy for nocturnal insects more broadly, because they remain within a few meters of where they hatched during the larval stage of their lives, before they acquire the ability to fly.
The team either struck the hedges with sticks so that the caterpillars fell out, or swept the grass with nets to pick them up.
The results were eye-opening, with a 47 percent reduction in insect population at the hedgerow sites and 37 percent reduction at the roadside grassy areas.
The lighting also disturbed their feeding behavior: when the team weighed the caterpillars, they found that those in the lighted areas were heavier.
The team found that the disruption was most pronounced in areas lit by LED lights as opposed to high-pressure sodium (HPS) lamps or older low-pressure sodium (LPS) lamps, both of which produce a yellow-orange glow that is less like sunlight.
there are really quite accessible solutions,” said Boyes—like applying filters to change the lamps’ color, or adding shields so that the light shines only on the road, not insect habitats.