Streetlights, particularly tremendous brilliant LEDs, might hurt insect populations

Moths flock to street lamps, enchanted by their glowing shine. But bathing in brightness all night seems to have consequences for the grounded forms of these fliers. Illuminated sections of English streets housed up to 52 percent fewer caterpillars than adjacent dark spots, researchers reported in Science Advances on August 25. Street lights could help reduce insect populations in developed areas, the researchers say.

Artificial light is generally not good for nocturnal insects. More recent work suggests that the glow can mess up the pairing or disrupt pollination (SN: 13.05.15; SN: 02.08.17). But whether night lights are contributing to population decline has not been researched enough, says Douglas Boyes, an entomologist at the UK Center for Ecology and Hydrology in Wallingford, England.

Boyes and colleagues compared 27 stretches of road that looked identical, except that some parts were lit at night and others were dark. Instead of looking at moths that can fly kilometers in the course of their lives, the researchers counted caterpillars that only travel a few meters. At night, the team cut dozens of species from roadside hedges or swept larvae out of grass and caught nearly 2,500 caterpillars.

Hedges under bright LED light contained 52 percent fewer caterpillars than dark sections, while areas under duller sodium lights contained 41 percent fewer. On grassy sections, LED lights reduced the population by 33 percent, while sodium lights had little effect. LED lamps emit a wider spectrum of light than other lamps, which could explain their increased impact. Caterpillars were thicker in lighted sections, which likely indicates abnormal development, Boyes says, but how exactly LED light harms caterpillars remains unclear.

The UK’s moth population has shrunk by a third in 50 years, but with less than 3 percent of the country under strong lighting from street lights, habitat loss and climate change are more likely than lights to be responsible, says Boyes. Still, the work shows a relatively easy way to give some insects a break, he says. Just turn the lights down or put filters on LEDs that will limit the spectra of light they shine down.