Horsfield's tarsier (Tarsius bancanus or Cephalopachus bancanus), also known as the western tarsier, is a species of tarsier. It occurs on Borneo, Sumatra, and nearby islands.
The taxonomy of this species is in doubt, with some subspecies considered unsure. In fact, over 20 years few studies have been done on T. bancanus and a taxonomic revision based upon intensive and systematic field surveys is overdue. The IUCN believes that these subspecies should be treated as distinct and named as separate taxa until more definitive evidence is available.
This species is a carnivorous species. It mainly eats insects such as beetles, grasshoppers, cockroaches, butterflies, moths, praying mantis, ants, phasmids, and cicadas, but also will eat small vertebrates such as bats (Chiroptera) including members of the Taphozous genus, the Lesser Short-nosed Fruit Bat (Cynopterus brachyotis), and the Spotted-winged Fruit Bat (Balionycteris maculata), and snakes, of which poisonous snakes have been found to be consumed. For example, the poisonous snake Manticora intestinalis was found to be hunted for by this species. This species was also found to consume birds, including: spider-hunters, warblers, kingfishers, and pittas. It locates prey primarily by sound and catches the prey with its hands when foraging. The prey items get killed by bites to the back of the neck and the eyes are shut when attacking. It will consume the prey starting with the head and working its way down the body. This species gets water both by drinking from a pool or steam, and by licking drops from bamboo leaves or from trunks of trees when water is running down the bark.
Infants are born with their eyes open and fully furred and are able to groom themselves. The mother will carry her infant in her mouth and when she forages for food the mother will park the infant on a branch. Infant sounds are mostly clicks: "k", "tk", "ki", or a rapid "kooih" and can be heard when the infant is left alone or is cold. The mother stays in contact with their infants using high-pitched calls. Infants were found to first use the tails as support during resting at 7–10 days. Young leave their range at the onset of puberty, and find their own territory.