Abstract: The effect of tourism on the distribution of larval blackflies during three different seasons of Palni hills wasinvestigated. Six streams were selected (Kumbakkarai, Moolayar, Kurusedi, Silver cascade Pampar and Guntar) for thisstudy, of which, three streams (Silver cascade Pampar and Guntar) were in peak of Palni hills (Kodaikanal town areas)and easy access to the tourists. The remaining three streams (Kumbakkarai, Moolayar and Kurusedi) were in downhillareas. The physico-chemical and stream parameters analyses indicated that the most tourist accessible site of Silver cascadestream had poor water quality and the predominant of larval blackfly population when compared to other samplingstreams. The highest population of larval blackflies was observed during winter followed by summer and northeastmonsoon. Since the effect of tourism causes pollution to streams, which in turn to promote the population of blackflylarvae and affect the other insect community in streams.