Artificial nighttime lighting is suppressing moth activity - University of Exeter

Moths move significantly less when exposed to artificial nighttime light, new research shows.

Moths’ attraction to artificial light, such as streetlights, is common knowledge and has been much studied. But, as many people will have observed, moths may also remain still if they land near a light, apparently “trapped”.

To understand this behaviour, University of Exeter researchers caught more than 800 moths from 23 species and exposed them to LED lights (of various colours and brightness) or to natural night conditions.

Moths were collected with light traps and butterfly nets on the Penryn Campus grounds, then placed outside in individual pots exposed to one of the light conditions, and filmed to record their movements overnight.

Under 10 lux – a level you might experience near residential streetlighting – moths moved 85% less on average than moths in natural nighttime conditions. This is a big impact on how moths behave, with implications for the time they have for essential activities like finding food or mates.

This could be because the artificial light confuses the moths’ sense of time, causing them to remain still as they do in the daytime, or because the light interferes with their vision.

The study also found that, at that same 10 lux intensity, amber lighting – commonly thought to be less harmful to insects – reduced moth movement just as much as typical white LEDs.