Street lights – especially those that use white light emitting diodes (LEDs) – not only disrupt insect behavior, but are also a culprit for their declining numbers, a new study in southern England showed on Wednesday. Artificial lighting at night had been identified as a possible factor in the decline in insect populations around the world, but the subject had been under-explored. To answer the question, scientists compared 26 roadside spots, made up of either hedges or strips of grass and lit by street lamps, with an equal number of almost identical spots that weren’t lit. They also examined a site with one unlit and two lighted sections, all of which were similar in vegetation.
The team chose moth caterpillars as proxies for nocturnal insects in the broader sense, as they stay just a few meters from their hatch during the larval stage of their life before they can fly.
The team either hit 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 populations in the hedge locations and a 37 percent reduction in the roadside grassy areas.
“We were really surprised at how strong it was,” lead author Douglas Boyes of the UK Center for Ecology and Hydrology told AFP, adding the team had expected a more modest drop of about 10 percent.
“We think it is most likely that it is because of the females and mothers who do not lay eggs in these areas,” he said.
The lighting also interfered with their eating behavior: when weighing the caterpillars, the team found that the caterpillars were heavier in the illuminated areas.
Boyes said the team interpreted this to mean that the caterpillars did not know how to react to the unfamiliar situation, which contradicts the conditions they have evolved over millions of years and, as a result, eat more food to accelerate their development .
The team found that the interference was strongest in areas lit by LED lights, as opposed to high pressure sodium (HPS) lamps or older low pressure sodium (LPS) lamps, both of which were amber-orange Luminaires produce lights that are less similar to sunlight.
LED lamps have become increasingly popular in recent years due to their superior energy efficiency.
The paper acknowledged that the effect of street lighting is local and makes a “minor contribution” to the decline in insect numbers, along with other important factors such as urbanization and habitat destruction, intensive agriculture, pollution and climate change.
But even localized reductions can have cascading effects across the ecosystem, resulting in less food for the birds and bats that hunt insects.
Additionally, “there are really easy-to-come-in solutions,” Boyes said – like applying filters to change the color of the lamps or adding shields so that the light only shines on the street, not insect habitats.
Read all the latest news, breaking news and coronavirus news here
