After three months, the belly and chest are dark reddish-brown, throat, cheeks, forehead and tip of tail are white and the rest of the body is jet black.

[9][11] The langurs sleep in the mid-upper levels of these trees above 20 metres (66 ft), where the canopy density is thickest, with the most common sites being in coconut groves.

The langurs move by quadrupedal running and climbing; they also leap in the mid and upper portions of the canopy and drop when nearer to the ground.

[2] Mentawai langurs spend more than 80% of their time resting and foraging and only a small portion traveling and conducting social behavior.

Such extensive periods of resting and foraging are required for colobines that consume seeds, unripe fruits and leaves to support their digestion.

In some areas, their diet consists of 55% leaves, 32% fruit and seed and 13% other source of food such as flowers, bark, sap, and fungi.