An insectivore by design
The Sri Lankan sloth bear (Melursus ursinus inornatus) specializes in myrmecophagy—the consumption of ants and termites. Unlike most other bears that are generalist omnivores, the sloth bear has a suite of specific physical adaptations for an insect-based diet. Its long, sickle-shaped front claws, which can be 6–8 cm long, are not for fighting; they are for ripping into rock-hard termite mounds. Once a mound is breached, the bear employs a unique and noisy feeding technique. It blows away dirt and debris, then uses its specialized mouth as a powerful vacuum.
This vacuum-like suction is made possible by several anatomical features. Sloth bears lack the two upper middle incisors, creating a perfect gap for sucking up insects. They also have a long snout, a hollowed-out bony palate, and mobile, protrusible lips that form a nozzle. To avoid inhaling dust while feeding, the bear can voluntarily close its nostrils. The loud slurping and sucking sounds made during this process can be heard from a great distance. This insect-focused diet is so effective that termites and ants can make up over 90% of their food intake, particularly during seasons when fruit is scarce.
A seasonal shift to fruit
While termites are the main part of their diet, sloth bears in Hurulu Forest and across Sri Lanka show a seasonal shift. When the fruiting season arrives, typically from April to August, these bears develop a powerful craving for sugary, high-energy fruits. Scat analysis—the primary, non-invasive method for studying their diet—shows a dramatic increase in the presence of seeds during these months.
Two fruits are important: Palu (Manilkara hexandra) and Weera (Drypetes sepiaria). Palu is a small, olive-shaped berry with a sweet pulp, and its fruiting season generally runs from June to August. The Weera fruit is a small, orange-to-red berry that fruits from April to September. The availability of these fruits is essential for the bears' health, allowing them to build up fat reserves. Researchers use the proportion of seeds to insect exoskeletons in bear droppings to track these dietary changes and monitor the health and fruiting patterns of the forest itself. A poor fruiting season can place stress on the bear population, forcing them to rely solely on insects or to forage in areas with more human activity.