Nighttime Streetlights Are Stressing Out Urban Insects

12:10 minutes

two large pink and tan moths clinging to someone's fingers

Standardized monitoring has revealed that the total number of moths has declined steadily by one third over the last 50 years (1968–2017). Pictured are two of the 2,500 moth species found in the UK (Left is a Elephant Hawk-moth, and right is a small Elephant Hawk-moth). Credit: Douglas Boyes

As insect populations—including bees, moths, and other pollinators—decline worldwide, researchers have established a variety of potential causes, including climate change, pesticides, and habitat loss. But now, new findings suggest yet another culprit may be part of the equation: night-time lighting, like street lights in populated areas.

A team of entomologists in the United Kingdom looked at populations of moth caterpillars under street lights, compared to populations that lived in darkness all night. In conditions with night-time lighting, they found nearly half as many caterpillars, in some cases. In addition, caterpillars that grew up under street lights were bigger, suggesting that they might be stressed and attempting to rush into metamorphosis earlier than they should. Furthermore, the greatest threat seems to be coming from energy-efficient LED lights, whose bluer wavelengths may be more stressful than the warmer, redder light of older sodium bulbs.

a round-about intersection that is brightly illuminated by led streetlights

LED streetlights at a rural junction in Curbridge, Oxfordshire. Credit: Douglas Boyes

a person in a bright yellow jacket and orange pants swings a bug net along the side of a brightly lit road in the middle of the night

Sampling nocturnal caterpillars in grass margins using a sweep net under white LED street lights in Golden Balls Roundabout, Oxfordshire. Credit: Jacob Jaffe

The team published their work in the journal Science Advanceslate last month. Guest host Umair Irfan talks to co-author Douglas Boyes about why nighttime lighting might be so bad for insects, and why ditching LED lights isn’t actually the best solution.

a collection of live caterpillars and moths in a cloth net, lit under LED lights

A selection of moth caterpillars caught by sweep netting under streetlights (mix of several species, family: Noctuidae) during fieldwork at night. Credit: Douglas Boyes

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