The brown spider monkey or variegated spider monkey (Ateles hybridus) is a critically endangered species of spider monkey, a type of New World monkey, from forests in northern Colombia and northwestern Venezuela. Like all spider monkeys, it has long, slender limbs and a long prehensile tail. The brown spider monkey has a whitish belly and patch on the forehead, and – highly unusual among spider monkeys – its eyes can be pale blue. The brown spider monkey is one of the most threatened primates in the Neotropics and has been listed six times on The World's 25 Most Endangered Primates. Taxonomy Some scientists recognise two subspecies, Ateles hybridus hybridus, found in both Colombia and Venezuela and Ateles hybridus brunneus, found between Cauca and Magdalena River in Colombia. Molecular studies have not supported the subspecies designations and treat the species as a single taxon. Physical description The brown spider monkey has long and thin limbs with longer forelimbs than hind limbs. It has a distinctive long flexible, thin and prehensile tail which at times acts like a fifth limb. The tail has a highly flexible, hairless tip with skin grooves which improves grip. Its fingers are curved and it has small thumbs. These features make it possible for it to climb trees at high elevations, and hang and swing from one tree to another without often having to return to the ground. Adult males weigh between and adult females weigh between . Its average adult body length is . Its coloration ranges from light brown to dark on upper parts including the head. Its most distinctive characteristic is a whitish triangular forehead patch, although not all individuals have one. Some have pale blue eyes but most are brown. Distribution The brown spider monkey is found in northern Colombia and northwestern Venezuela. In Colombia, it is found from the right bank of the Magdalena River in the Magdalena and Cesar Departments, the south western portions of Guajira in the northernmost parts of the Serrania de Perija, and in the middle Magdalena River Valley at least to the Caldas and Cundinamarca Departments. In Venezuela, the brown spider monkey is normally found at altitudes between . Ecology and behaviour Even though the brown spider monkey spends most of its time high in trees, it occasionally descends to eat soil and drink water. Since it forages in high canopies, it prefers undisturbed primary forests. The