Quirks & Quarks

Streetlights — especially new LEDs — can drastically reduce caterpillar numbers

A recent study looking at how artificial light affects insects in England showed that areas lit by streetlights showed much fewer caterpillars living therein, and eco-friendly LED streetlights fared worse than traditional sodium lights.

Moth caterpillar numbers were 50 per cent lower in areas with LED streetlights along roads in the UK

Researchers sampling nocturnal caterpillars in grass margins using a sweep net under white LED street lights. The brightness and colour temperature of the lights is believed to affect moths because they mimic daylight and can disturb the insects nocturnal behaviours. (Jacob Jaffe/Douglas Boyes)

Editor's note: After broadcasting this interview, originally recorded in September, we were informed that Douglas Boyes had passed away. We offer our condolences to his family.

A recent study looking at moth caterpillars along roads in England has found that areas lit by eco-friendly LED (light emitting diode) streetlights had significantly fewer moths than in similar areas lit by traditional streetlights.

PhD student Douglas Boyes wanted to understand how artificial light might be tied to current insect population declines. In his study, he identified sites that had caterpillar habitat along stretches of road that had streetlights and then a stretch with no lights. Half of the streetlights were traditional sodium lighting, and the other half had LEDs.  LED lights tend to be more energy efficient and more durable than older light technologies.

"When we're looking at caterpillars, they don't really move more than a metre or so," Boyes told Quirks & Quarks host Bob McDonald. "So we can be really confident any effects we're finding are very much local."

A selection of several species of moth caterpillars caught by sweep netting during fieldwork. Researchers found significantly fewer caterpillars in areas lit by streetlights. (Douglas Boyes)

He found that in habitat consisting of hedgerows, there was a 51 per cent reduction in caterpillar numbers under LED streetlights, and 42 per cent reduction under sodium lights. In habitat containing grasses, there was a 33 per cent reduction for LEDs but no difference under the sodium lights.

"It was really a shocking result," said Boyes. "You don't really see those sorts of numbers that often in ecology. It's definitely a bit worrying."

He believes the drastic differences are because the LEDs tend to be significantly brighter than sodium lights, so they can mimic daylight and interfere with the moth's typical nocturnal behaviour. 

"One of the really nice things I think about this as a topic is that there are some really fairly accessible solutions," he said, suggesting that LEDs be dimmed, or changed to a different colour temperature, in order to reduce the effects on insects.

The study was published in the journal Science Advances.

Douglas Boyes is a PhD student in ecology with the UK Centre for Ecology and Hydrology. You can listen to his full conversation with Bob McDonald at the link above.


Written and produced by Amanda Buckiewicz.

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