Sumatran slow lorises are nocturnal, meaning they are awake and active from the time the sun goes down until it rises. They spend much of their time foraging, traveling, and hunting insects. They are primarily solitary primates, and when they encounter other lorises they whistle and hiss to denote their territory and presence. The Sumatran slow loris relies on its sense of smell more heavily than monkeys and apes. They utilize special scent gland scents to mark and stake their claim on territory. 

The Sumatran slow loris is highly arboreal. Often, they will use well-worn paths through the trees, and occasionally the ground. They tend not to sleep in the same location many times, as that leaves them vulnerable to predation.

Lorises have a unique adaptation to combat predation. They are the only primate in the world that is venomous! On the inside of their elbow, they have a gland that secretes a substance that, when mixed with the loris’ saliva, becomes toxic. They use this to protect themselves, and mothers use it to protect their young by bathing their babies in the toxic substance. The toxin produces an unpleasant and pungent smell, which also helps communicate the “keep away” message to would-be predators. If a large mammal were to be bitten, it would most likely result in severe illness and discomfort. Deaths have been recorded for larger animals when a bite is left untreated. 

If their environment gets especially cold, the loris might enter a state of torpor. Torpor is an extended period of rest that could last hours or a few days. This is not considered hibernation, though, as that behavior can last weeks or months. 

There is still much that researchers do not know about the Sumatran slow loris, primarily due to their nocturnality and the terrain they live in. It is quite difficult to accurately follow small, skilled arboreal primates in the dark!