Street lights have direct influence on insect populations

Changes reverberate up food chain

PARIS — Street lights have an unexpectedly strong effect on insect populations, favouring some species while punishing others, according to a study released Wednesday that raises new questions about human effects on wildlife.

Researchers led by Thomas Davies at the University of Exeter, southwestern England, spent three days in August 2011 placing insect traps around Helston, a small town in Cornwall. They picked up 1,194 insects from 60 different species.

Proximity to street lights was a big factor in the number of insects and the prevailing species, they found.

Five species, including ants, ground beetles and woodlice, were far more abundant in patches under street lights compared with patches between street lights. And street lights also drew more predatory and scavenging insects.

Tiny changes among insect populations reverberate up the food chain, boosting some species but imperilling others, the biologists note.

“Street lighting changes the environment at higher levels of biological organization than previously recognized, raising the potential that it can alter the structure and function of ecosystems,” says the study.

Street lighting is advancing at the average rate of six per cent worldwide each year, but its impact on wildlife is poorly understood.

Anecdotal evidence suggests street lights affect the body clock of urban birds, tricking them into feeding longer, and on the feeding habits of mammals such as foxes, rats, mice and bats.

The paper, published in the British journal Biology Letters, voices concern about the introduction of next- generation street lighting that uses metal halide or light- emitting diodes.

These technologies emit light over a broader range of wavelengths to which organisms are sensitive, it says.

“The paucity of information available on the environmental impacts of artificial light pollution does not currently reflect the potential scale of this problem.”