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Ecological zones The distribution of butterflies and dragonflies is influenced by temperature, rainfall, altitude and the geology of the land. Sri Lanka has traditionally been divided into five broad ecological zones–the arid zone, the low-country dry zone, the low-country wet zone and the central hill zone with a transitional intermediate zone between the lowlands and the hills. There are also tracts of grasslands which are of secondary origin in the hills that are home to some species of butterflies, though not exclusively. The mangroves and salt marshes are not specific to any species of butterfly but certainly offer excellent habits for some species. The Low-Country Dry Zone: The low-country dry zone occupies about three-quarters of the country. It receives between 25-75 inches of rain, most of which falls towards the end of the year. Elevation ranges from sea level to 500 feet above sea level. It is hot and dry for most of the year. Rice is cultivated extensively under irrigation from man-made water reservoirs that are called tanks. Vegetables are also cultivated in this zone after the monsoonal rains. It does have some tracts of forest and scrub jungle, though vastly reduced from its former size due to new settlements. Most of the butterflies found in this zone are similar to those in South India.
The Low-Country Wet Zone: It lies to the south-west of the central hills and comprises of a small area of densely covered low hills. It is generally hot and humid throughout the year with some parts receiving over 200 inches of rain per year. Most endemic species of butterflies are found in this zone.
The Central Hill Zone: It contains the central mountain cluster and outlying highland ridges. The higher altitudes, up to about 9,000 feet, are sometimes subject to frost. Rainfall ranges from 80 to over 200 inches per year. Tea is widely cultivated in the higher elevations. The lowest number of butterfly species is encountered in this zone, though a few are endemic.
The Intermediate Zone: This is a transitional zone between the plains and the hills and is intermediate in climate often has considerable species overlap. The intermediate zone is much wetter in the north west than in the south east. This zone is the richest in terms of butterfly diversity.
The Arid Zone: Two small areas confined to North West and South East of the island receiving less than 25" of rain, mostly towards the end of the year followed by a long stretch of drought. Though alike in many ways, there are species that are confined only to one and not the other. Some species of butterflies are found only in these two zones and nowhere else in the island.
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Ecological Zones