The otherwise pitch-black nights in the Manambolly forests in the Anamalai Tiger Reserve (ATR) along the Western Ghats in Tamil Nadu are witnessing a mega light show of bioluminescence.
Several lakhs of fireflies, perched on trees and shrubs, are emitting lights synchronously, turning the forests into a magical world of yellowish-green glow. A team, comprising ATR Field Director S. Ramasubramanian, Deputy Director Bhargava Teja, Assistant Conservator of Forests V. Selvam and members of the Wild and Dark Earth (WiDE), an NGO engaged in the study and conservation of nocturnal habitats, recorded the rare phenomenon in the Manambolly range mid-April, after studying fireflies and their life cycle in the tiger reserve for a year.
Last year, Mr. Ramasubramanian and Sriram Murali of WiDE, who is also part of the IUCN Species Survival Commission Firefly Specialist Group, recorded a similar synchronised lighting of fireflies in the Ulandy forest range of the ATR.
Mr. Murali and Chandrasekar Rathnam, co-founders of WiDE, spent several nights in the field, documenting and researching firefly diversity, their life cycle, ecology, and factors affecting their populations.
According to Mr. Murali and Mr. Rathnam, firefly larvae start emerging in the wet, evergreen forests after the first summer rain. Fireflies live as larvae for a year before they pupate and become the adult. “Firefly larvae glow to warn predators and use bioluminescence as a defence mechanism. The larvae depend on moisture to prevent them from desiccating. They are voracious predators and feed on soft-bodied insects such as earthworms, snails and slugs,” said Mr. Murali.
Mr. Murali explained that the larvae go through a stage of pupation to become the adult fireflies with wings after a year of growing. As adults, fireflies seldom eat, besides despising sunlight and resting in shaded areas during the day.
“As adults, fireflies have one purpose — to mate. Fireflies flash to communicate, especially to find mates. Studies have shown that synchronised displays of fireflies are more attractive to females and easier to identify their own species in crowded areas,” said Mr. Rathnam. After mating, female fireflies lay eggs and the whole cycle continues again. Even the eggs display bioluminescence.
Formed in 2022, WiDE is mapping firefly populations in India, and the ATR has been identified as one of the hotspots. Mathi Thumilan and Sreedhar P.S., the other co-founders of WiDE, develop scientific approaches towards conserving fireflies and raising awareness of the wonders of the dark and the ill-effects of light pollution.
According to the founders, WiDE is collaborating with Forest Department officials and scientists at the Advanced Institute for Wildlife Conservation (AIWC), Chennai, to identify the species diversity of fireflies through DNA extraction and sequencing to understand the impact of light pollution on fireflies.
In the ATR, WiDE discovered that firefly larvae feed on leeches. The WiDE study found that firefly larvae eat 5-10 insects every night. The study presumes that a reduction in the firefly population may lead to an exponential increase in leech populations, affecting the entire ecosystem. Some studies have indicated that leeches can have a negative impact on native wildlife species.
The WiDE’s study in the ATR also showed that fireflies detest white light and go for shade when they are exposed to it. It found that artificial lighting hampered the ability of fireflies to communicate and mate, thus causing a decrease in their populations. The teams at the WiDE and the AIWC are researching the impact of different wavelengths of lights on firefly larvae and adults.
“Populations of fireflies are on the decline across the world. Mega congregations in large areas of the forest are very rare. It is a major feat to document them in yet another range in the ATR, which is also a testament to the years of conservation efforts by the Forest Department,” said Mr. Ramasubramanian.