Earthworm Mass Migration and Associated Mortality in Kerala Part of the Western Ghats Biodiversity Hotspot

Earthworm migration in significant quantities is an extremely rare event in nature. The probable cause for such migration and associated mortality is generally obscure without additional information on the bio-ecology of the region. The present study was conducted as a result of public reporting of mass migration and mortality of earthworms in two hilly districts of Kerala, namely Idukki and Wayanad (part of Western Ghats biodiversity hotspot) following the worst deluge for decades in Kerala, 2018 (August-September). The major aim of the study was to find the species involved and probable cause for this mass migration and death of earthworms in the reported regions. Dead and dying earthworms were collected from the sites of mass death by hand picking, digging and hand sorting methods. Our examination revealed that a total of four species of earthworms viz., Amynthas alexandri Beddard, 1901, A. corticis (Kinberg, 1867), Metaphire houlleti (Perrier, 1872) and Pontoscolex corethrurus (Müller, 1857), belonging to Megascolecidae and Rhinodrilidae families were found migrating and dead in masses at these sites. All the species that underwent mass migration and mortality were naturalised exotic species. It can be inferred that the native species are more accustomed to the changing weather pattern in the region. The physical characteristics and the sudden change in moisture content of the soil seem to have triggered the mass migration and associated mortality of earthworms in the Western Ghats of Kerala.