Ever seen a monkey with glasses? Visit the forests of Northeast India, and you might catch a glimpse. The Phayre’s leaf monkey stands out among India’s primates for its striking facial markings—a dark face framed by white rings around the eyes and lips, giving it a bespectacled look. Even among local communities in the forests of Tripura, Mizoram and southern Assam, where the monkey is found, the primate is known as chasma bandor (in Bengali) and chasma-chakuwa bandar (in Assamese).
The primate’s other physical features also pique fascination. Its thick bluish-grey coat turns slightly brownish on the body and limbs, while a slender, long tail—often longer than the body—helps it balance as it moves among treetops. Adults weigh 6-8 kg, with males slightly heavier. Both sexes have a small sagittal crest on the head, forming a triangular silhouette when seen from below. Infants are born with a golden-yellow coat, making them easily visible within the troop. The colour darkens gradually, a trait shared by several colobine or leaf-eating monkeys of Asia.
The langur is arboreal and diurnal, and lives in cohesive groups typically led by a dominant male. A group’s size can range from five to 30 individuals depending on habitat quality. The groups are highly territorial, using vocal calls, postures and coordinated displays to defend their ranges.
The primate is named after Arthur Purves Phayre, a 19th century British officer and naturalist. The species, Trachypithecus phayrei, was first described in 1847. But in recent years the monkey was genetically reclassified, as scientists discovered that what was believed to be Phayre’s leaf monkeys across India and Myanmar are separate species. The Indian population of T phayrei is now known as Phayre’s langur, while that seen in Myanmar is now called Popa langur (T popa). This revision implies that the actual population of Phayre’s langur is lower than previously estimated, intensifying conservation concern.
Like several primates, Phayre’s langur has seen a sharp population decline due to habitat loss, forest fragmentation and hunting, and is now listed as Endangered on the International Union for Conservation of Nature Red List. The threats it faces have now manifested change in the primate’s behaviour. For instance, although it prefers evergreen and semi-evergreen forests or moist deciduous woodlands, it can now also be seen residing in secondary forests such as bamboo clusters and rubber plantations.
Rapid habitat alteration has led to notable dietary shifts. A strict folivore, the Phayre’s langur feeds primarily on young leaves, shoots, and flowers, occasionally consuming fruits and seeds. Its specialised multi-chambered stomach enables it to digest fibrous leaves efficiently, contributing to nutrient cycling and seed dispersal in the ecosystem. Studies in Sepahijala Wildlife Sanctuary show that the monkey’s diet now includes leaves of rubber, posing a significant health risk due to the presence of toxins that may adversely affect its gut health and overall physiology.
Protecting Phayre’s langur is critical not only for its survival but also for the forest ecosystems of the Indo-Burma biodiversity hotspot. It serves as an indicator species—its health reflects the condition of the forest canopy and the richness of plant diversity.
Conservation initiatives in Assam, Tripura, Mizoram, and Bangladesh are now focusing on habitat restoration and community engagement, encouraging local participation in protecting secondary forests and corridors between remaining habitats. The monkey is also recognised as Tripura’s state animal and was featured as the mascot of the 2024 North East Youth Festival to highlight its conservation needs.
This article was originally published as part of the December 16-31, 2025 print edition of Down To Earth