Colombo, Nov 08 (Daily Mirror) - Large swarms of white and yellow butterflies spotted across several parts of Sri Lanka in recent days are part of a natural seasonal migration triggered by monsoon rains and the growth of host plants, experts have explained.
The sightings, reported in areas including Ratnapura, Galle and Colombo, have attracted considerable attention on social media, with some questioning whether the unusual movement signals an approaching natural disaster.
However, research and expert observations indicate that the phenomenon is a recurring migration within the island, mainly involving butterflies of the Pieridae family.
A field study conducted by the Department of Zoology at the University of Peradeniya identified two main migration periods in Sri Lanka: the principal migration season from October to December, during the Second Inter-Monsoon, and a smaller migration period from March to April during the First Inter-Monsoon.
Butterfly expert Himesh Jayasinghe explained that monsoon rains encourage the growth of host plants, providing fresh leaves for caterpillars and suitable conditions for butterflies to lay eggs. The resulting increase in butterfly populations prompts them to disperse in search of food and breeding grounds, reducing competition for resources.
Research conducted by Prof. Kapila Dissanayake and a team from Sabaragamuwa University, published in the Taprobanica Journal in 2024, identified three migratory species: the Lesser Albatross (Appias galene), Common Albatross (Appias albina) and Lemon Emigrant (Catopsilia pomona).
Based on observations at 60 locations across the island, the researchers identified three main flight paths, with the principal migration route running from the southeast towards the northwest, from Kebiliththa in Kumana National Park towards Wilpattu.
The butterflies travel at an average speed of around 11 kmph, covering the approximately 280-kilometre journey in three to four days.
Experts said the traditional belief that butterflies migrate towards Sri Pada also has a scientific explanation. The behaviour, known as 'hill-topping', involves butterflies gathering at elevated locations such as Sri Pada and Kirigalpoththa, where changes in elevation and temperature help them locate potential mates.
However, field studies indicate that most Albatross butterflies migrate towards the northwest rather than Sri Pada.
Experts have also dismissed claims that large butterfly migrations are warnings of impending natural disasters, saying there is no scientific evidence to establish such a connection. Although butterflies are sensitive to atmospheric pressure, humidity, temperature and wind changes, their movements cannot be considered an official warning of cyclones or other disasters.
Meanwhile, researchers have observed a decline in butterfly populations and migration activity compared with the past. Irregular monsoon patterns linked to climate change can disrupt breeding cycles, while invasive plants such as Guinea grass and Gandapana (Lantana camara) have affected native host plants, including Thora species.
The destruction of these plants threatens migratory butterfly species by reducing the availability of suitable breeding and feeding grounds.
The former president of the Butterfly Conservation Society of Sri Lanka said the October-November transition between the Southwest and Northeast monsoons creates favourable conditions for the growth of host plants in the dry zone, encouraging butterfly populations to increase and spread across the island.
She said the recent sightings were part of this natural internal migration, rather than an arrival of butterflies from overseas.
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