Unusually for monkeys, they don't have thumbs (but they still have opposable big toes). The lack of thumbs on their hands is thought to aid their movement through the forest. In fact, the name "colobus" is thought to come from the Greek word "kolobus" meaning maimed or mutilated, due to their missing thumbs.
The colobus monkeys eat leaves almost exclusively, only occasionally taking in fruits and flowers. Their stomachs are very large, with three separate chambers that help to ferment and digest the leaves, very similar to the process of rumination in cows. They have been recorded to eat 46 different species of plant, but only five species make up the greatest proportion of their diet.