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Season of butterflies
By K.G.H. Munidasa
November to December is the period of butterflies. Their season comes towards the end of the year, for it is during this period of monsoonal rains that the vegetation is green and fresh, affording the insects excellent egg-laying sites and an abundant food supply.

A most amazing natural phenomenon that fascinates everyone during this time of the year is the mass cross-country migration of various species of butterflies. Impelled by some mysterious instinct, thousands of these scaly-winged creatures can be observed flitting past in an unbroken stream.

In multitudes they come and go for hours and days or even weeks on end, looking for all the world like a thin hailstorm. In a broad front they fly, in home gardens, on the roads, over paddy fields and shrub jungle, across lagoons and tanks, making their aerial way to an unknown destination.

Very little is really known regarding these cross-country flights of the butterflies which are always in one direction, the return flight not undertaken as far as records show. What causes the insects to start migrating or how they keep to a more or less constant direction are secrets no one can fathom. What stops the migration at last is yet another perplexing subject.

In the Dry Zone it has been observed that the mass movement begins around the last week of October, grows in intensity during the first three weeks of November and then decreases towards the end of the month. However, in a lesser degree it will continue in December or occasionally in the months of March, April and May.

In Sri Lanka some 69 forms are listed as 'flighters' but in the main the majority that migrates in a given period appears to belong to the group 'peirids', mainly of a white colour or nearly so, with sprinklings of other types taking part.

Once in the Eastern Province I observed a mass movement in the month of November in which over 90 percent were Common Indian Crows flying steadily in a northerly direction, while in the meantime another column of peirid butterflies were cutting diagonally across the former in a northeasterly direction.

In Sri Lanka the flights are in various directions in different places. But they appear to be towards the southeast or northeast in the Eastern Province (Ampara) and mainly towards the west, southwest or occasionally northeast in the Walawe Valley (Timbolketiya) and the adjacent Hambantota coast. In the Kelani Valley (Avissawella) it has been found to be between north and south or occasionally towards the southwest.

These hordes of butterflies generally start moving around 8.30 or 9.30 in the morning when the sun is sufficiently high in the sky, coming to a peak about 10 to 11 o'clock, if it is bright weather and continue till about 2.30 or 3.00 p.m. Clouds covering the sun's rays or a sudden shower of rain will stop the migration altogether, to be resumed once the sun shines again.

As far as records go, no convincing explanation, based on scientifically proven facts, has so far been adduced for the annual migration of the island's butterfly. Some hold the view that these great swarms are pilgrims on their way to the Holy Mountain (Adam's Peak) in the centre of Sri Lanka, while others believe they are simply overflow-movements, for there is evidence that a migration is often preceded by a surplus of caterpillars.

But whatever the assumption may be the very fact of its being shrouded in mystery heightens our wonder and enjoyment of this annually recurring phenomenon that is butterfly migration.

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