Biodiversity at Risk: Examining the Decline of Swallowtail Butterflies due to Host Plant Overexploitation in Assam

Swallowtail butterflies (family: Papilionidae) are vital indicators of ecosystem health, with their presence and diversity closely tied to the availability of specific host plants for their larvae. This study examines the alarming decline of swallowtail butterfly populations in Assam’s Bodoland Territorial Region, an area renowned for its rich biodiversity and often referred to as the “citrus belt of the world.” The overexploitation of 25 species of host plants, many of which are valued for their traditional medicinal properties, is identified as a significant factor contributing to this decline. Field surveys conducted in the Manas Biosphere Reserve documented 4,267 individual butterflies representing 35 species across eight genera. The study highlights that the overharvesting of key plant species, particularly those in the Rutaceae, Aristolochiaceae, Lauraceae, and Magnoliaceae families, has led to a marked reduction in the availability of essential larval food sources, with profound impacts on butterfly populations, particularly in the Papilio, Atrophaneura, and Graphium genera. The findings also underscore the role of habitat degradation, including illegal cattle farming, deforestation, and pesticide use, in exacerbating the loss of biodiversity. The study observed the absence of rare species such as the Bhutan glory (Bhutanitis lidderdalii) and the Kaiser-i-Hind (Teinopalpus imperialis), which may be linked to the diminished availability of host plants. This paper argues for urgent conservation efforts focused on restoring and protecting critical host plants and habitats, recognizing their integral role in maintaining the ecological balance and long-term survival of these globally endangered butterflies. Recommendations for sustainable management practices and policy interventions are provided to ensure the preservation of both swallowtail butterfly populations and their host plants within this ecologically sensitive region.