Slow lorises vary in colour from grey to white depending on their range. They are plumper and shorter-limbed than slender lorises. They have strong grasping hands and feet, with opposable thumbs. Slow lorises have dark rings around their eyes and a dark stripe running along the backThey are nocturnal and arboreal. They spend the day sleeping in a tight ball up a tree, with their head between their thighs, but become active at sunset. They are thought to be solitary, and males have larger ranges than the females. Slow lorises make a buzzing hiss sound when disturbed. They move quadrupedally and slowly through the forest.