A wild orangutan named Rakus treated a facial wound with chewed leaves
In 2024, a wild Sumatran orangutan called Rakus was seen chewing leaves of the plant Fibraurea tinctoria and smearing the paste onto a wound on its face. Weeks later it appeared healed. Such inventiveness runs through the species, which carries toolkits, uses leaves as umbrellas and talks entirely in gestures.
Found only in northern Sumatra, this critically endangered ape numbered roughly 13,846 in 2017. Males reach about 1.7 metres and 90 kilograms, females about half that weight. Compared with their Bornean cousins they are slimmer, longer-faced and paler red, eat more fruit and insects, and spend more time up in the trees, perhaps because Sumatran tigers prowl below. They are the heaviest mammals to travel through the canopy, swaying flexible trunks back and forth to reach the next support.
In the Suaq Balimbing swamp they are gifted toolmakers. An orangutan snaps off a branch, strips the twigs and frays one end with its teeth to probe for termites or honey. Neesia fruit hides tasty seeds among irritating, glass-like hairs, so the apes use a short stripped stick to scrape the hairs away first. Useful tools are kept, building up whole toolboxes. Bornean orangutans in similar swamps have not been seen doing this.
Communication is silent. Researchers have catalogued 64 gestures, 29 with meanings other orangutans usually understand, such as play, stop, share food or move away; Sumatran orangutans do not use sounds, not even alarm calls. They are also more sociable than Bornean apes, gathering in loose groups at fruiting fig trees.
Their lives are slow. Mothers give birth on average every 9.3 years, the longest gap of any great ape, and youngsters stay close for years. Wild females live roughly 44 to 53 years. When fruit runs short they occasionally eat slow lorises. Their genome, sequenced in 2011 from a captive female named Susie, showed that Sumatran and Bornean orangutans split about 400,000 years ago, and that Sumatra's apes are genetically more diverse despite being far fewer.
Source: Sumatran orangutan
