Residents across Kolkata have been witnessing an extraordinary natural spectacle throughout November, with thousands of small brown butterflies appearing suddenly across the city. From residential balconies and gardens to pavements and even indoor spaces, these delicate creatures have become an unavoidable presence in daily life.
What Species Are These Butterflies?
According to butterfly experts, the species creating this remarkable phenomenon is the Common Evening Brown (Melanitis leda). Each tiny flier weighs just a few milligrams and spans approximately 2.5 to 3 inches, with their leaf-like appearance making them masters of camouflage until they emerge in large numbers.
Tollygunge resident Sourav De expressed his amazement at the unusual sight. "Quite unusual," he described, noting the surge over the past fortnight. "I haven't seen anything like this before. Friends and relatives are noticing the same thing," said the independent film-maker, echoing the observations of many Kolkatans.
Why The Sudden Butterfly Explosion?
Arjan Basu Roy, a butterfly expert with 25 years of experience, provides scientific insight into this natural occurrence. The prolonged monsoon and post-monsoon rainfall have created ideal conditions for the butterflies' host plants to flourish. "The abundant grass growth has provided perfect breeding conditions. Without these ideal circumstances, the butterflies would have remained dormant as pupae," explained Basu Roy, who curates butterfly conservatories in Eco Park, Banabitan, Buxa and Rajabhatkhawa.
Another contributing factor could be a decline in natural predators like ants, wasps and spiders, though this theory requires evidence-based confirmation through proper scientific study.
Butterfly Lifecycle and Behavior Patterns
The Common Evening Brown follows a predictable lifecycle that explains their sudden appearance and disappearance. The complete lifecycle from egg to adult takes approximately one month, progressing through egg, larva, pupa and adult stages. The adult butterflies live for only about two weeks, which accounts for their brief but noticeable presence.
Navneet Singh, a lepidopterist at Zoological Survey of India, explains their attraction to human habitats: "These butterflies develop in low-light conditions and gradually get drawn to indoor lighting, which explains why people encounter them inside homes, parks and other well-illuminated areas."
The butterfly's remarkable camouflage contributes to the illusion of sudden emergence. "They perfectly mimic dead leaves in color, pattern and shape," said Amlan Das, senior entomologist at Calcutta University. "When they appear in large numbers, their camouflage effectiveness decreases, creating the impression that they've materialized everywhere at once."
Ecological Significance and Reassurance
Dhriti Banerjee, director of Zoological Survey of India, assures residents that there's no cause for alarm. This represents a recurring seasonal event rather than an ecological warning or invasion. "The species typically experiences population peaks at winter's beginning," she confirmed.
This year's particularly mild temperature fluctuations in Kolkata—characterized by warm days and cool nights—have further enhanced the butterflies' mobility and visibility.
Despite their overwhelming numbers, these butterflies pose no nuisance. The caterpillars feed exclusively on common grasses, while the adult butterflies serve as important prey for birds, reptiles, spiders and small mammals. Additionally, the adults function as effective pollinators, contributing positively to the urban ecosystem.
The last comparable butterfly emergence in Kolkata occurred in 2019, making the current spectacle a relatively rare natural event that residents can appreciate without concern for their gardens or homes.
