February 2015 Featured Paper

"Impact of Artificial Light on the Distribution of the Common European Glow-worm, Lampyris noctiluca" by Stefan Ineichen and Beat Rüttimann. Lampyrid: The Journal of Bioluminescent Beetle Research, Volume 2 (December 2012), pp. 31-36.
Read the Original Paper. (Subscription to Lampyrid is required. Check your local university library for access.)

Firefly experts believe that artificial lights in the evening have an effect on firefly mating behavior. However, to date, there have been no field studies to support this belief. This study investigates the effect of artificial evening light on the common European glowworm, Lampyris noctiluca.

L. noctiluca are native to Europe and Asia. When the larvae are ready to pupate, they seek out open areas bordered by low vegetation where adult females can be seen by males in flight. Larvae must select unobstructed locations because adult females have small, non-functioning wings and cannot fly to be visible. Female larvae choose their display site during the day when no artificial light is present, with the result that adult females will be found in both lit and unlit areas along the street.

Mating is triggered by decreasing ambient light levels. As evening falls, females climb nearby vegetation and begin to emit a constant glow. Males have no light organs and cannot produce light, so unlike flashing fireflies where the males display to attract a female, these females must glow to attract the males.

The study area is a residential street in Switzerland. Five street lights produce cones of light on the ground, with darkness between these illuminated spots. Over the course of this study, 31 females were found displaying under the lamps and 76 females were found in the dark in-between zones.

Males patrol the open area searching for glowing females. LED light traps made to mimic the glow of the female were set up both under the street lights and in the dark interspatial areas. The number of males attracted to these traps was then recorded. Tests were conducted both on nights when street lights were lit (11 trials) and on nights when they were off (3 nights).

Results

On evenings when the street lamps were on, 73 males were trapped in the dark sections between lamps. None were caught in the well-lit sections directly under the lamps. On evenings when street lights were off, 58 males were trapped both beneath and between lamps.

These results indicate that light pollution from street lamps does indeed have a negative effect on the ability of fireflies to mate successfully. Either artificial light interferes with the male’s ability to see a glowing female, or males may avoid illuminated areas altogether. In either case, females in the artificially illuminated areas die without ever mating.

In the test area, enough fireflies mated in the dark zones that the lighting seems not to have negatively affected the local population as a whole. It is possible that a well-planned residential area with both lit and unlit zones might be able to support a healthy firefly population.


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