LED streetlights reduce insect populations by 50% - UK Centre for Ecology & Hydrology

‘Eco-friendly’ LED streetlights are even more harmful for insect populations than the traditional sodium bulbs they are replacing, a new study has shown.

The negative impacts of light pollution on insects including moths - which provide essential food sources for a variety of animals and are important pollinators - are well known. However, scientists behind this latest research say it is the first investigation into the effects of the whiter outdoor LED lights on insect populations in ‘real world’ conditions.

A selection of caterpillars from a sweep net sample for the study. Pictures: Douglas Boyes
A selection of caterpillars from a sweep net sample for the study. Pictures: Douglas Boyes

Field studies by the UK Centre for Ecology & Hydrology (UKCEH), Newcastle University and Butterfly Conservation found the abundance of moth caterpillars in hedgerows under LED street lamps was 52 per cent lower than in nearby unlit areas. This compared with a 41 per cent lower abundance in hedgerows lit by sodium lighting.

Meanwhile, in grass margins, the moth caterpillar numbers near LEDs were a third lower than in unlit areas, whereas sodium lights had little effect on abundance in this habitat.

Almost all previous research on light pollution has focused on adult insects, but studying caterpillars, which are a lot less mobile, enables researchers to get more precise estimates of the impacts of street lighting on local populations. The authors add the large diversity of moths means they are broadly representative of nocturnal insects, with any negative impacts from a threat likely to also be experienced by other species.

Douglas Boyes of UKCEH, who led the study, published in the journal Science Advances, spent more than 400 hours sampling for caterpillars along roadsides at a total of 55 lit and unlit sites in the Thames Valley over the past three years.

He says: “The effects observed – on local abundance, development and feeding behaviour – were more pronounced for white LEDs compared to traditional yellow sodium lamps. The rapidly increasing prevalence of LED lights, which are often much brighter as they are so energy-efficient and cheap to run, is likely to increase the negative impacts of light pollution on insects. This is expected to have knock-on effects on other species, including predatory insects, hedgehogs, and songbirds, which need to find hundreds of caterpillars a day to feed themselves and their young.”

Read the paper: Douglas H. Boyes, Darren M. Evans, Richard Fox, Mark S. Parsons, Michael J.O. Pocock. 2021. Street lighting has detrimental impacts on local insect populations. Science Advances. DOI: 10.1126/sciadv.abi8322

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