Butterflies of Sundarbans

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Prevalence of diverse range of climatic conditions and eventually the floral and faunal distribution in India and neighbouring environment has acclaimed the nation to be recognized as Indian Subcontinent. Existence of tropical evergreen & deciduous forest, hot desert, temperate forest, polar vegetation in the Himalayas and mangroves in the estuaries of Bay of Bengal has supported for the sustenance and growth of rich biodiversity in our homeland. It is very necessary to know how and what extent various kinds of interdependent relationships maintain a balance in nature. Concept and approach of Biodiversity conservation must not be limited for the gigantic mammals but should be included the small sized life creatures like butterflies, spiders, ants, dragon flies etc. As per the wildlife habitat new approaches have been adapted as per Wildlife Protection Act, 1972 for maintaining wildlife habitat.

Sundarban is the last remaining largest mangrove forest of the world with rich ecosystem and immense diversity, spread over 10,200 sqkm. across the delta of the river Ganges, Brahmaputra and Meghna on the Bay of Bengal. The mangrove ecosystem of Sundarban is the home to a diverse types of aquatic and terrestrial plants and animals.

Butterflies being important part in the food chain act as a source of food for various predators and an important media of plant pollination. In the recent years butterflies are considered as a focal species for biodiversity conservation in different parts of the world. It's not possible to identify and estimate the change of butterfly community over the time period until and unless enough database of butterfly is available from the Sundarban Mangrove Biosphere. The Sundarbans, in spite of being a unique deltaic region with rich bioresources presents insufficient documents on butterflies.

The Sundarbans region stretches along the coast of Bangladesh (6,017 km2) and India (4,000 km2) and forms the largest single block of halophytic mangrove forest in the world. The Sundarbans is one of the richest ecosystems in the world harboring high levels of floral and faunal diversity representing around 785 floral and 2091 faunal species, including the home to one of the largest and most unique populations of tigers in the wild.

One of the global biodiversity rich regions and the World Heritage Site, the Indian Sundarbans faces existential threats especially climatic and demographic challenges. The estimated cost of environmental damage associated with ecosystem degradation and biodiversity loss in the Indian Sundarbans, is about INR 6.7 billion per year and the total loss of ecosystem service valuation was estimated 3310.79 million USD during last 45 years.

In Indian Sundarbans the class insecta was represented by 753 species which included 210 lepidopteran species under 24 families and 161 genera. Of these lepidopteran species 115 are of butterflies under 06 families and 85 genera. Indeed, mangrove ecosystem would not function without insects. So, the study of insect diversity became a prime interest of research, because the group dominate terrestrial and freshwater ecosystems and are valuable indicator of their health. The butterfly was originally named 'flutterby', may be due to their fluttering habit in a flower garden. Worldwide, there are more than 28,000 species of butterflies, with about 80 per cent in tropical regions. Because of its need to feed on nectar, butterfly plays an important role in ecosystems, acting as a pollinator. Increased butterfly population may indicate an increase in plant diversity and other pollinator groups within restored areas. Hence extensive studies of these eye-catching colorful insects are needed for their conservation to keep the ecosystem healthy and functional.

The name Lepidoptera, which comprises moths (Heterocera) and butterflies (Rhopalocera), was first used by Linnaeus in 1735. It described all species of butterflies under the genus Papilio and all species of moths under the genus Phalaena and Noctua. The order Lepidoptera, which includes butterflies and moths, was the last of the winged insects to emerge on the evolutionary pathway after flowering plants some 160 million years ago. These insects have a broad variety of wing patterns and colour, ranging from dull moths like the adjacent order Trichoptera (Caddisflies, water moths), to brightly colourful and intricately patterned butterflies (Ghosh et al., 1991).

The members of the order Lepidoptera characterized by two pairs of membranous wings, contain a long-coiled proboscis as one of their mouth parts, which differentiate them from other groups of insects. The setae (macrotrichia) covering the wing membrane have become modified into flattened, overlapping scales. Majority of the lepidopteran scales are present on the head, thorax, legs, and abdomen. These scales, through pigment or structure, contribute colour and pattern to the wings, perform some aerodynamic function, and may provide a limited means of thermoregulation. Lepidoptera, in particular, has high species richness and abundance and they significantly respond to idiosyncratic climate and abiotic factors, which make them potential indicator taxa for studies focusing on environmental impact.

The term "Rhopalocera" is used to species of butterflies on the shape of their club shaped antenna. They belong to the holometabolous (life stages with egg, larva, pupa & adult) endopterygote (wings develop internally) insects. Probably, the butter-yellow colour of the Common Brimstone male (Gonepteryx rhamni Linnaeus, 1758) of the family Pieridae is the source of origin of the term "Butterfly" (Ghosh et al., 1991). Butterflies are the most important component of our biodiversity.