Web of Life

In Sri Lanka, November to December is the season of the butterflies. It is in keeping with the fitness of things that their season should be towards the end of the year, for it is during this period of island-wide rains that the vegetation is at its best and the tender foliage affords the insects ample egg-laying sites and an abundant food supply for the caterpillars.

One of the most fascinating natural phenomena to be observed during this time of the year is the mass cross-country migration of various butterflies. Impelled by some mysterious instinct, thousands and thousands of these 'joyous little beings' can be seen flitting past in an unending stream.

In countless numbers they come, winging their way a few feet above the ground, and go on for hours and days or weeks on end, looking for all the world like a thin snow-storm. In a broad front they advance, in home gardens, on the highways, over paddy fields and scrublands, across lagoons and tanks, threading their aerial way to an unknown destination.

L.G.O.Woodhouse, in his Butterfly Fauna of Ceylon, quotes from a published source an observation in Colombo on October 25, 1895 which runs as follows," I certainly thought I had stepped into the land of butterflies. The harbour, streets and large promenade, the Galle Face by the sea shore were alive with butterflies and being nearly comprised of Catopsilia (whites) looked like a snow-storm."

Miss Gordon Cumming, author of 'Two Happy Years in Ceylon' commenting on the periodical movements of the butterflies in Sri Lanka observes:- "One of the mysteries of the Isle is the annual migration in November to December and at intervals right on until February, of countless myriads of butterflies in vast flights. The migration commences with the setting in of the North-East monsoon with its cool mornings and bright days, and the stormy winds blowing stronger, these delicate insects force their way against it and in a couple months, successive legions pass on like an over-flowing stream."

Very little is really known regarding these mass movements of the butterflies, which always seem to be in one direction. What causes them to start migrating? There is evidence that the migration is often preceded by considerable over-crowding of the caterpillars. It is not known how these dainty creatures keep to a more or less constant direction, or what makes them after all to resume a normal life once again.

No scientific explanation has so far been adduced, as far as I am aware, for this periodical migration of the butterflies in Sri Lanka. Even that eminent naturalist Sir Emerson Tennent, once referring to the uninterrupted passage of these insects in a north-easterly direction has said, "Whence coming no one knows; whither going, no one can tell."

In extensive studies carried out by this author in the Eastern, Southern, Sabaragomuwa and Western Provinces, over a period of 10 years, it has been found that the flights began about the last week of October and grew in intensity during the first three weeks of November and then decrease towards the end of that month. However, on a lesser scale, movements of the insects continued sporadically through December and January to March or even June. In 1975 in the Eastern Province, a thin migration was observed as early as the third week of September.

The flights are generally in various directions in different places. But they appear to be towards south-east or north-east in the Eastern Province (Hingurana, Ampara district), and mainly towards west, south-west or occasionally north-east in the Walawe Valley (Timbolketiya, Ratnapura district) and the adjacent Hambantota coast. In the Kelani Valley (Madola, Kegalle district) the direction of flight has been found to be between north and south, or very occasionally towards south-west.

In South India major flights are reported to be towards south in October-November, with a return flight north in February and March. No return flight appears to have been recorded in Sri Lanka.

In Sri Lanka 69 forms of butterflies are listed (Woodhouse- 1949) as 'fighters', but in personal experience, the majority that migrate in a given period appear to belong to the family Pierids, for the most part white or creamish-white in colour, e.g. Pioneer, Common and Lesser Gulls, Common and Lesser Albatrosses, Common and Mottled Emigrants, with sprinklings of Common Leopard, Chocolate Soldier, Common Indian Crow, Blue, Glassy and Dark-blue Tigers, Peacock Pancy, Common Banded-Peacock, Common and Blue Mormons, Common and Tailed Jays, Grass Yellow, Dark Wanderer, Common Birdwing and Lime butterflies.

In November 1972 at Muwangala (E.P.) a mass movement in which over 90 percent were the Common Indian Crow was observed. While these in a broad front moved steadily in a northerly direction another column of Pierid butterflies was cutting through them in a north-easterly direction. This continued for a full week.

Three days later a similar movement was observed at Timbolketiya (Uda Walawe, Ratnapura district), but there about 90 percent were either Common or Lemon Emigrants with sprinklings of the Common Indian Crow, Common Mormon, Pioneer, Blue Tiger etc. In the last week of the same month a mass movement of the Common Indian Crow was also observed in the Kelani Valley which lasted for six days.

There is no doubt that the very fact of it being shrouded in mystery, the migrational flight of the butterflies heightens our enjoyment and as well as wonderment of it.