The numbers of fireflies are going down, as a result of street-lighting that is too bright, according to a master’s thesis by a biology student at the university of Antwerp.
The process is simple: female fireflies – actually a kind of beetle also known as glow-worm or lightning bug – give off light from organs in their abdomen which is used to attract males of the species.
However in conditions of bright street-lighting, males are no longer able to distinguish the females, and so cannot mate with them.
“When the females of the firefly are close to street lighting, the males do not see that they are lit up. That way they are invisible and they can no longer reproduce. The LED lighting hides their pairing signals,” explained biologist Mira Van den Broeck on Radio 2 Antwerp.
The experiment took the form of a trap worthy of a Shakespearean comedy. Males were lured to the light of a green LED lamp, where they fell through a funnel into a vessel where they could be counted.
That process was carried out in various locations, so that the difference could be measured between bright light sources and less-bright. In locations where real females could still be spotted, the LED lure would be less successful.
The conclusion: fireflies prefer to do it with the lights off. And the quality of the light makes little difference: modern white LED lighting has the same deterrent effect as the old-fashioned orange street lamps.
The solution: dim the lamps during breeding season.
“Fireflies are mainly found in natural environments. Think of the edge of a forest, or rural areas with shrubs,” Van den Broeck said.
“If we dim the street-lights on those often traffic-calmed places in the mating season, we can save the firefly. That is from the end of June to mid-July. Another beautiful luminous species, the glow-worm, can also benefit from this. In Malderen they have already tried this out successfully.”