The effect of tourism on the distribution of larval blackflies during three different seasons of Palni hills was investigated. Six streams were selected (Kumbakkarai, Moolayar, Kurusedi, Silver cascade Pampar and Guntar) for this study, 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 downhill areas. The physico-chemical and stream parameters analyses indicated that the most tourist accessible site of Silver cascade stream had poor water quality and the predominant of larval blackfly population when compared to other sampling streams. The highest population of larval blackflies was observed during winter followed by summer and northeast monsoon. Since the effect of tourism causes pollution to streams, which in turn to promote the population of blackfly larvae and affect the other insect community in streams.