Globally, the firefly population has been under threat because of familiar subjects such as urbanisation and habitat loss as well as increasing use of pesticides, however, more recent studies have attributed the decrease in firefly population with artificial light at night (ALAN) (Dunham, 2020). One of the main impacts that ALAN has on these fireflies are its effects on the mating process.  

As seen from the comic above, fireflies are commonly associated with their light emitting bottoms found at their lower abdomen, known as lanterns. These bioluminescent fireflies use these flashing signals, also known as courtship signalling systems, to engage in sexual communication with potential mates (Owens, 2018). For example, the North American Photinus fireflies engage in courtship dialogs that requires accurately timed flash signals which communicates its species identity and sex to other fireflies (Owens, 2018). From the comic on the left, in the absence of light pollution, bioluminescence (the production and emission of light by a living organism) act as an effective visual signal in contrast to the dark surrounding (Cronin et al, 2000). Because of the temporality of their courtship activity, fireflies are very sensitive to ambient light cues which tell the time of the day. When ambient light intensity drops to a level that is within the specific species’ threshold, courtship signalling is being carried out (Owens, 2018). 

However with light pollution, Scientists in Maryland stated that with ALAN, there was approximately a 50% decrease in firefly flashes per minute. To put it simply, too much light reduces flash activity and also increases the difficulty for them to see each other’s signals. For example, one of the reasons that was attributed to the decline of the Lampyris noctiluca population, a species of firefly found in Europe, was that male fireflies were more attracted to particular sources of ALAN than they were to the glow signals that were given off by females (Owens, 2018). Additionally, because of ALAN, females are less responsive to male signals that are often perceived as dimmer compared to surrounding light sources. 

According to Bird and Parker (2014), orientation of light sources also has the potential to disrupt mating process, whereby upward-directed light increases the chance of males getting dazzled, resulting in lowered trap visibility compared to downward-directed light sources. Hence, these ALAN light sources have the potential to disrupt and mislead individuals from conventional forms in mating and can lead to the overall decrease in their population. 

Before you go, take a look at this video below which gives a visual representation on how these wonderful creatures light up at night to find their mates. Let’s continue to be mindful of the way we use our lights so that we don’t end up dimming the lights of such precious beauties of the night. 

 Stay tuned for more!

Jean

 

Reference List: 

• Bird, S., & Parker, J. (2014). Low levels of light pollution may block the ability of male glow‐worms (Lampyris noctiluca L.) to locate females. Journal of Insect Conservation, 18, 737–743 
• Cronin, T. W., Järvilehto, M., Weckström, M., & Lall, A. B. (2000). Tuning of photoreceptor spectral sensitivity in fireflies (Coleoptera: Lampyridae). Journal of Comparative Physiology A, 186, 1–12 
• Dunham, W. (2020). Reuters: Fireflies threatened globally, with light pollution a glaring problem. Retrieved from  http://www.reuters.com/article/us-science-fireflies-idUSKBN2012C7
• Owens, A. C. S., & Lewis, S. M. (2018). The impact of artificial light at night on nocturnal insects: A review and synthesis. Ecology and Evolution, 8(22), 11337-11358.
• Comic retrieved from https://www.greenhumour.com/2018/03/fireflies-and-light-pollution.html?m=1