The distribution of the Nilgiri langur (Semnopithecus johnii) a threatened colobine endemic to the southern Western Ghats and the hanuman langur (Semnopithecus priam) an endemic to south India and Srilanka abuts each other in some parts of their common boundary i.e. they show a parapatric distribution in the southern Western Ghats. There have been reports of hybridization between them in some areas. Natural hybridization has been reported between several primate species.

The Nilgiri langur (Semnopithecus johnii) and common langur (Semnopithecus priam thersites) are colobines found in the southern tip of the Western Ghats. Changes in land use patterns and the loss of habitat owing to the ever-increasing demand for land to meet anthropogenic requirements are major causes for these and other primates being critically threatened today. Data regarding patterns of parasitic infections in langur populations in the wild are a critical indicator of the population health and will mark a beginning towards assessment and management of disease risks.