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Slow loris

Conservation status:

Life span: 25 years (captive)
Total population: Unknown
Regions: Southeast Asia
Gestation: approx. 6 months
Height: N. coucang 27 to 38 cm, N. pygmaeus 19 to 22 cm
Weight: 265 to 1605 g

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Suborder: Strepsirrhini
Infraorder: Lorisiformes
Family: Lorisidae
Genus: Nycticebus
Species: N. bengalensis, N. coucang, N. javanicus, N. pygmaeus
Subspecies: N. c. coucang, N. c. menagensis

Other names: N. bengalensis: N. cinereus, N. incanus, N. tenasserimensis, Bengal slow loris, Bengal loris, northern slow loris; N. coucang: N. brachycephalus, N. buku, N. hilleri, N. insularis, N. malaiana, N. natunae, N. sumatrensis, N. tardigradus, greater slow loris, slow loris, Sunda slow loris; loris lent (French); loris lento (Spanish); tröglori (Swedish); N. c. menagensis: N. menagensis, N. bancanus, N. borneanus, N. philippinus, Bornean slow loris; N. javanicus: N. ornatus, Javan slow loris; N. pygmaeus: N. intermedius, pygmy slow loris, lesser slow loris, pygmy loris; dvärgtröglori, mindre tröglori (Swedish).

The taxonomy of the genus Nycticebus is fluid. At present, there are four species within Nycticebus, with only N. coucang separated subspecifically into N. c. coucang and N. c. menagensis (Groves & Maryanto in press cited in Chen et al. 2006; Chen et al. 2006). Some researchers consider N. c. menagensis as the full species, N. menagensis. It is considered as the subspecies N. coucang menagensis here (Nekaris et al. 2008).


N. coucang
Nycticebus coucang
Photo: Marilyn Cole

There is significant size variation across the genus Nycticebus, with some types (N. bengalensis) over two times the weight of other types (N. c. menagensis) (Ravosa 1998). Some of the size variation is clinal over the distribution of the genus, however N. bengalensis and N. pygmaeus are sympatric and N. pygmaeus is quite smaller than N. bengalensis (Ravosa 1998). Head and body length of N. coucang is 27-38 cm (10.6-15.0in) and N. pygmaeus is around 19-22 cm (7.5-8.7) (Rigel 2004; Ankel-Simons 2007; Streicher 2007). Recorded slow loris body masses are N. bengalensis (1134-1605g (40.0-56.6oz), N. c. coucang (599-685g (21.1-24.2oz)), N. c. menagensis (265-300g (9.3-10.6oz)), N. javanicus (565-687g (19.9-24.2oz)), and N. pygmaeus (418-422g (14.7-14.9oz)) (Nekaris et al. 2008). Male and female N. pygmaeus do not differ significantly in head and body length, while they do in body weight, with males weighing somewhat more than females (Kappeler 1991; Streicher 2007). However, N. coucang do not show sexual dimorphism by weight (Kappeler 1991).

In general, there is a whitish strip between the eyes, starting on the forehead and continuing until the end of the nose. The head is round and the ears are hidden in thick fur which characterizes slow lorises as a whole. The tail is reduced to a stump and is also hidden in the fur (Ankel-Simons 2007). The eyes are large (Choudhhury 1992). The second digit is short, and the hand performs as a powerful clamp for grasping (Ankel-Simons 2007). N. coucang has light brown pelage, with a dark stripe down its back (Groves 2001). N. javanicus is yellow-gray with a dark to black stripe down its back. N. bengalensis is orange-buff or warm orange, with a grey neck and a thin brown stripe down its back (Duckworth 1994; Groves 2001). Overall, N. pygmaeus is dull reddish, medium to dark brown and gray-brown with very thick fur, and is darker dorsally than ventrally (Duckworth 1994; Groves 2001; Streicher 2004b; Ankel-Simons 2007). It is also important to remember however, that there are seasonal changes in pelage coloration in N. pygmaeus (Streicher 2004b). Slow lorises have glands on their elbows that secrete a strong-smelling liquid used in communication (Hagey et al. 2007).

Movement is typically slow, with three limbs almost always in contact with whatever the loris is moving on (Wiens 2002; Rigel 2004). Slow lorises are capable of quadrupedal movement, both above, and while suspended from, a support in their environment (Ishida et al. 1986). In captivity, movement (N. coucang) is quadrupedal (24%), climbing (21%), suspension (including cantilevering) (29%), bridging (23%), and in other forms of locomotion (3%) (Gebo 1987). Slow loris movement is a unique type of quadrupedalism, which is very deliberate (almost reminiscent of crawling or as if the animal was climbing in any direction it is moving), changing direction or moving between supports without much noise or change in speed (review in Jouffroy 1989). Lorisids, including Nycticebus do not leap between supports and are almost fully arboreal, rarely coming to the ground (Curtis 1995; Huynh 1998).

In captivity, members of the genus Nycticebus have lived up to a little over 25 years (Weigl 2005).


Nycticebus bengalensis | Nycticebus coucang coucang | Nycticebus coucang menagensis | Nycticebus javanicus | Nycticebus pygmaeus

In general, slow lorises are found in southeast Asia, ranging from eastern India (east of the Brahmaputra River) to Indochina and southern China south to the Malay peninsula and Java, Borneo and the far western Philippine islands (Simunul, Bongao, Sanga Sanga, and Tawitawi) near Borneo (Groves 1971; Zhang et al. 1981; Fooden 1991). N. bengalensis has the largest range of the genus, and is found in Myanmar, Cambodia, southern China, northeast India, Laos, Thailand, Vietnam, and Bangladesh (Khan & Ahsan 1986; Haque & Siddiqi 1988; Brandon-Jones et al. 2004; Nekaris & Bearder 2007; Nekaris et al. 2008). N. c. coucang is found in Indonesia, the Malay peninsula (Malaysia) and Thailand. N. c. menagensis is found in Brunei, Indonesia, Malaysia, and the far southwestern Philippines (Fooden 1991; Brandon-Jones et al. 2004; Nekaris et al. 2008). N. coucang is also found in Singapore (Nekaris et al. 2008). N. javanicus is only found on Java, Indonesia. Finally, N. pygmaeus is found in eastern Cambodia, south China, Laos, and Vietnam (Brandon-Jones et al. 2004; Nekaris et al. 2008). N. pygmaeus and N. bengalensis are sympatric, and have distributions that overlap in Laos, Vietnam, and southern China (Duckworth 1994; Wiens 2002). In general, it appears that slow lorises are rare in many areas of their distribution and are not always easily found even within their known range (Nekaris & Nijman 2007).


Reflecting their large distribution overall, slow lorises are found in a range of habitats including tropical rainforests to seasonal forests including tropical evergreen and semi-evergreen forests, seasonal wet evergreen, dry evergreen forest, mixed deciduous tropical forest, sub-tropical broadleaf hill forests, swamp forests, savannah, montane and submontane forests, shrub forests, peat swamp, primary forests and hardwood forests, as well as degraded habitats such as highly disturbed forests, secondary forests, disturbed primary forests and logged forests (Barrett 1981; Choudhury 1992; Duckworth 1994; Huynh 1998; Wiens et al. 2006; review in Nekaris et al. 2008). N. bengalensis prefers bamboo forest mixed with hardwood trees, farmbush and mangrove swamps, as well as peat swamp forest and low and tall interior forests while N. coucang is found in continuous canopy tropical rainforest (Nekaris & Bearder 2007; Nekaris et al. 2008). N. pygmaeus is found in bamboo forest mixed with hardwood trees, forest edge habitats, and dense scrub (Nekaris & Bearder 2007). The exact habitats of N. javanicus and N. c. menagensis are unknown (Nekaris & Bearder 2007).

At one long-term study site on the western coast of the Malay Peninsula, Malaysia, yearly rainfall averages 178.5 cm (70.3in), usually with a rainy season (Oct-Dec) and a dry season (Jun-Jul) (Wiens 2002; Wiens et al. 2006). At this site, the average annual temperature is 26.7°C (80.1°F), with little variation over the course of the year (Wiens et al. 2006).


N. coucang
Nycticebus coucang
Photo: J. R. Mackinnon

At one study site in western Malaysia, slow lorises (N. coucang) spent their feeding time eating sap (34.9%), floral nectar and plant parts that produce nectar (31.7%), fruit (22.5%), and the rest gums and arthropods (including insects and spiders) with little seasonal change in proportions (Wiens et al. 2006). In a different short term study of reintroduced individuals, the pygmy loris (N. pygmaeus) ate 40% insects, 30% gum, and 30% other exudates (Streicher 2004a). Insects are caught in one or two hands, sometimes with the animal gripping its support bipedally. Exudates are ingested by licking trees, especially around wounds oozing gum (Streicher 2004a). There is some evidence to suggest that N. pygmaeus may purposefully gouge trees to induce the flow of exudates for consumption (Tan & Drake 2001).

Slow lorises are a nocturnal species, starting their nightly activity around sunset (Wiens 2002; Choudnury 1992). They have an extremely low metabolic rate relative to other mammals of their size and live a slow lifestyle (Wiens et al. 2006). Over the course of the night, most (93.3%) of their time is spent solitary. Feeding averages around 20.5% of the daily nightly activities with resting comprising only around 5.4 % (Wiens 2002).

Slow lorises (N. coucang) sleep during the day, rolled up in a ball in hidden parts of trees above the ground, often on branches, twigs, palm fronds, or lianas (Choudhury 1992; Wiens 2002). N. bengalensis sleeps often in tree holes or in dense brush, while N. coucang do not (Choudhury 1992; Wiens 2002). Individuals usually sleep alone but also occasionally sleep with other slow lorises, including other adults (Wiens 2002). Estimates indicate that an individual slow loris may use around sixty individual sleeping sites (Wiens & Zitzmann 2003b).

Recorded home ranges are highly variable, even within a single species (N. coucang). Recorded home ranges of this species range from 0.004 km² to 0.25 km² (0.0015 to 0.1 mi²), with significant overlap among adults (Wiens 2002; Wiens & Zitzmann 2003b). In one study, the average home range in forests was 0.034 km² (0.01 mi²), while in savanna the value was 0.148 km² (0.06 mi²) (Wiens & Zitzmann 2003b). The average home range of N. pygmaeus is 0.03 km² (0.01 mi²) (Nekaris & Bearder 2007).

Pythons (Python reticulatus) are a confirmed predator, as are hawk-eagles (Spizaetus cirrhatus) and orangutans (Pongo pygmaeus) (Utami & van Hooff 1997; Wiens & Zitzmann 1999; Hagey et al. 2007). Civets and owls do not elicit a response from slow lorises nor do the predators react to their presence (Wiens & Zitzmann 1999). Predatory attacks on slow lorises are avoided primarily through crypsis (Wiens & Zitzmann 1999; 2003b). Other methods of escape include merely falling away from the threat by releasing its support, biting (which can be painful) or rolling up in a defensive posture with the arms over the head and with elbow gland oils spread on its back (Tenaza & Fitch 1984).

Sympatric N. bengalensis and N. pygmaeus have been seen to forage simultaneously in the same tree, within several meters of one-another (Duckworth 1994).

Content last modified: March 18, 2009

Written by Kurt Gron. Reviewed by Helena Fitch-Snyder.

Cite this page as:
Gron KJ. 2009 March 18. Primate Factsheets: Slow loris (Nycticebus) Taxonomy, Morphology, & Ecology . <>. Accessed 2014 April 16.