Insects act in coordination with natural light regimes and are sensitive to changes in light intensity, wavelengths, sources and other factors.
Nocturnal insects perform various activities such as foraging, reacting to predators, or navigating using the stars and moon. For insects of the family Lampyridae, commonly known as fireflies, low light is needed for reproduction.
The month of June is considered the best time to spot these bioluminescent creatures, as it is an important breeding season. Maharashtra hosts firefly festivals in May and June, which are celebrated by the local communities and wildlife enthusiasts as well as photographers from different parts of the country. However, this congregation of Lampyridae is affected by the increasing urban lights, impacting their numbers.
Fireflies vs artificial light
Fireflies use their bioluminescence, a chemical reaction that produces light, for mating communication. Adults of one or both sexes (depending on species) emit specific flash patterns which are received by the other sex. During the mating season, fireflies flash late in the day, shortly after sunset, when light levels are low. High levels of artificial light can inhibit this signalling activity.
In the presence of artificial light, fireflies are forced to expend more energy in trying to flash brighter and have their signals noticed by prospective mates, although the effects vary among species which are receptive to different wavelengths.
According to a 2018 study on Aquatica ficta fireflies, commonly found in Taiwan and parts of China, the intervals between flashes become much higher, as fireflies try to flash brighter to compete with artificial light. This reduces their chances of finding a mate and negatively affects reproduction rates.
Fireflies are highly sensitive to ambient light cues, since their courtship activities are restricted to specific times of the day. Nocturnal insects in general are adapted to natural light regimes, so they are extremely sensitive to artificial light which can disorient, attract, repel, or blind them. While there is limited data available on the populations of nocturnal and bioluminescent insects, researchers around the world have observed the declining presence of insects such as fireflies. Light pollution, then, becomes a matter of ecological concern.
Fireflies are found in temperate and tropical regions in wetlands and marshes near wooded areas. Firefly adults are short-lived, with life spans ranging from a week to a few months.
Compared with other countries, fireflies have not been well-studied in India. There is very little data on the exact population occurrences. In one study, a researcher, Ramesh Chatragadda, from the National Centre for Coastal Research attempted to record the population of Abscondita chinensis firefly species in a specific area in Andhra Pradesh.
In the study village, Barrankula, fireflies in a 10-meter area went from 500 in 1996 to 10-20 in 2019. The exact reasons for this decline are difficult to determine, considering that only two counts were recorded, 23 years apart. The local communities, however, confirm that they have witnessed a stark decline in the firefly population.
According to another survey in 2020, that attempted to understand the global perspective on firefly extinction threats, the most serious threats (pdf) to fireflies noted by experts are habitat loss, light pollution from artificial light at night, and pesticides—in that order. The researchers conducted the survey of experts from diverse geographic regions to identify the most prominent perceived threats and only two of the 49 experts who responded were from south Asia; but they conceded that habitat loss and pesticides are the greatest threats.
Although pesticides are seen to be a central factor in fireflies’ declining occurrences, light pollution is a major contributor as evidenced by a separate study (pdf) on the species Photinus sp1, conducted in Brazil. Researchers in this study found that firefly occurrences (as observed by their flash patterns) depend on proximity to light. They studied three different area transects, at 60, 150, and 280 metres from the main artificial light source: four spotlights with three multi-metal vapour lamps each. They observed a significant difference in the number of fireflies. The closer one went to a light source, the lesser fireflies there were.
These findings from the Brazil study are significant, as they evidence the direct correlation between the number of active fireflies and distance from artificial light. With the reduction of dark areas in the world, fireflies are facing greater and greater habitat loss, making light pollution a significant threat to their population.
As fireflies’ populations are decreasing, they might be endangered, with several species on the verge of extinction—if not extinct already. Studies and monitoring efforts have been scarce, especially in India. One of the main reasons for this lack of research is because photo-pollution or light pollution is difficult to measure. The precise ways in which it affects different populations, especially nocturnal and bioluminescent species, is difficult to study too. More research is needed to document the species and their behaviour changes to artificial light.
What is the role of fireflies in an ecosystem?
Fireflies’ luminescent genes have several applications in medicine, food safety testing, and forensics. More importantly, however, an ecosystem is made up of interconnected parts. Each link in the chain depends on the other, and the loss of each species weakens the links.
Plants and animals carry out different processes that affect other species directly or indirectly. Firefly larvae feed on snails, slugs, mites, and earthworms, keeping their population in check. An excess of these invertebrates, damages vegetation growth. This affects the wildlife that feeds on that vegetation. The snowball effect is vast environmental damage. Fireflies, like other species, maintain a delicate balance in the ecosystem.
This post first appeared on Mongabay-India.