Wild monkeys in Sumatra are part of the island's rich biodiversity. They usually belong to such breeds as the long-tailed monkey (Macaca fascicularis) and the siamang (Symphalangus syndactylus). These monkeys live in dense tropical rainforests, from lowlands to mountains. They are known for their agile, intelligent nature, and have high social abilities.

Sumatran wild monkeys are often seen clustered in trees, foraging for food such as fruits, leaves, and insects. However, as their habitats are threatened by deforestation and human activities, some species are experiencing significant population pressures. They also sometimes approach settlements in search of food, which can lead to conflicts with humans. Their presence reflects the importance of maintaining ecosystem balance in Sumatra.