Washington (AFP)

Street lighting is not good for insects.

In addition to disrupting their behavior, it can go as far as directly reducing their number, according to a study conducted in the south of England and the results of which were published Wednesday in the journal Science Advances.

The researchers studied in particular the caterpillars of moths.

They only move a few meters around the place of their hatching and their population can therefore be easily studied very locally.

A total of 26 sites lit at night were studied - hedges or grassy areas by the roadside.

Each of them was compared to an unlit and not very distant site, presenting the same characteristics (vegetation, town planning, etc.).

Samples of caterpillars were taken, either by shaking the hedges and recovering the larvae that had fallen, or using a net.

Photo of moth caterpillars provided by the lead author of the study showing that city lighting harms Douglas Boyes caterpillars www.douglasboyes.co.uk/AFP

As a result, the caterpillars were on average 47% less numerous in the hedges, and 33% less abundant in the grasses.

"We were all amazed that it was so striking," Douglas Boyes, lead author of the study and researcher at the UK's Center for Ecology and Hydrology, told AFP.

Rather, a reduction of around 10% was expected.

"The most likely explanation is that females do not lay their eggs in these areas," he explains.

"It is not a behavior that they have in the light."

These nocturnal animals have been used to darkness "for millions of years" so "this light is unusual, it's new," he says.

Photo taken in Curbridge, Oxfordshire, UK, provided by the lead author of the study showing that street lighting is harming Douglas Boyes caterpillars www.douglasboyes.co.uk/AFP

It also disrupts their life cycle: each caterpillar was weighed and those taken from the lit areas were heavier.

"They precipitate their development" by eating more and faster, because the situation seems "dangerous or unusual" to them, explains Douglas Boyes.

The researchers also showed that the reduction in the number of caterpillars was greater under streetlights using LED bulbs - whiter and therefore more similar to daylight - than under conventional sodium bulbs (HPS).

However, LEDs are used more and more because of their better energy performance.

The study acknowledges that "street lighting has probably contributed only a minor way to the long-term decline of moths at the national level".

But this light has "all the same a very important local effect".

And cascading consequences: fewer caterpillars means less food for birds or bats.

However, there are "very accessible solutions", underlines Douglas Boyes.

By installing, for example, colored filters or screens directing the light only on the roads.

© 2021 AFP