The migrating butterflies
An interesting annual phenomenon under study
The iridescent, velvety wings flutter around in swarms: the seasonal visitors are here again. For a few years now, during the period December-February, a throng of butterflies have made their appearance in pockets of Visakhapatnam district. Environmentalists and nature-lovers are monitoring the phenomenon.
"We have been observing this peculiar behaviour of the crow and tiger butterflies," says Prof. M. Rama Murty of the Dolphin Nature Club, a founder-member of the biodiversity park at the RCD Government Hospital here.
A recent study by environmental organisations showed that the "tiger" and "crow" butterflies have a tendency to migrate in large groups from the Western Ghats to the Eastern Ghats during certain periods of the year. Such arrivals have been observed also in Bangalore, Tumkur and Mysore in Karnataka; Palakkad and Kannur in Kerala; Coimbatore, Udhagamandalam, Vellore and Chennai in Tamil Nadu, and Tirupati, also in Andhra Pradesh. It has been witnessed also in some wildlife sanctuaries.
The insects migrate in clusters and for a specific period remain rooted to a spot, where they copulate. "Interestingly, migration of butterflies is different from that of birds since the ones that return are not the original butterflies," says Mr. Murty. The long-distance migration can be attributed to a combination of climatic factors, food availability and breeding habitat preferences.
"The most obvious cause for migrations is a rapid expansion of the population of one or more species in an area leading to reduced food supply," Mr. Rama Murty says.
The migration route is yet to be determined. The groups consist of over 20 species .
The migration of the North American Monarch butterfly from Canada and northern United States to Mexico in autumn and the return journey in spring is well known. In India, larger-scale migrations occur in the Western Ghats. "In southern India, butterfly migrations have been documented in the Palni Hills and places like Assam and Rajasthan. Twenty-two species are known to migrate, travelling south in October during the rainy season," says Prudhvi Raj of the Wildlife Institute of India, Dehra Dun.
But why do the butterflies flock to only certain plants? "The males, on emerging from their pupae, lack certain chemicals essential to the process of courting females. Butterflies need pyrrolizidine alkaloids for the production of these sexual pheromones and these are obtained from plants such as Crotalaria, Heliotropium and Senecio subdiscoideus," says Mr. Raj.
Some action patterns are observed, including `mud-puddling', wherein the butterflies land on wet mud and suck salt and other minerals and nutrients from the soil.
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