Slow loris


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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).

Conservation status:  multiple

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

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).


Slow loris in tree

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).


Slow loris feeding

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 2020 July 9.


The N. c. coucang social system might be closest to a monogamous single male/single female social system with the pair living with offspring (Wiens & Zitzmann 2003b; Nekaris & Bearder 2007). In one study, slow lorises (N. coucang) were predominantly solitary, spending only around 8% of their active period near other slow lorises. If an individual slow loris home range overlaps with that of another, encounters are generally friendly, but not so if there is no range overlap. These friendly relations define “spatial groups” which are a unit of social organization in the species. In general, only four types of interaction are seen on a nightly basis among slow lorises in the same “spatial group.” These include allogrooming, following, pant-growling, and click-calling, and social behavior only make up around 3% of the activity budget (Wiens & Zitzmann 2003b). In captivity, allogrooming is also the most common social behavior (Newell 1971). In addition, not all individuals are members of a spatial group. Home ranges are not defended, and neither are food patches. When members of a spatial group encounter non-members, there is usually no interaction (Wiens & Zitzmann 2003b). While usually alone, adult slow lorises will sometimes sleep with up to several conspecifics, including other adult animals (Wiens 2002).

Slow loris in tree

Social behaviors in varying contexts have been recorded in artificial groups of captive N. coucang. In fact, when kept together in captivity, they are quite sociable, although adult males can be very intolerant of one another and may fight, often resulting in serious injury (Ehrlich & Musicant 1977; Tenaza & Fitch 1984). In captivity, agonistic behaviors include attacks, pursuits, threats, assertion, fighting, and subordinate behaviors. Associative behaviors include close proximity, physical contact, following, social exploration, social grooming and social play (Ehrlich & Musicant 1997). In a different captive study, severe aggression included threats and attacks, and less intense aggression (staring, cringing, pant-growling and avoidance) was also seen (Daschbach et al. 1982-1983). Dominant or submissive behaviors among slow lorises are not seen in captivity (Rasmussen 1986).

In general, slow lorises disperse around 16-27 months of age, and both sexes have been seen dispersing in the wild (Wiens & Zitzmann 2003b).



The true mating system of wild slow lorises is unknown, and may in fact be variable between populations (Wiens & Zitzmann 2003b). However, it might be best described as a monogamous single male/single female social system (Wiens & Zitzmann 2003b; Nekaris & Bearder 2007). In one anecdotal observation, several male slow lorises were seen to follow a female and attempt to mate with her (Elliot & Elliot 1967).

N. pygmaeus females show sexual swelling during estrus, during which the genitals turn reddish. Females also show behavioral estrus, increasing their approach, departure, and lunge behaviors during estrus (Fitch-Snyder & Jurke 2003). N. coucang however, only rarely show these sexual swellings (Zimmermann 1989). Males pursue estrus females around (Fitch-Snyder & Jurke 2003). Estrus cycles in N. coucang last 29-45 days, averaging 36.4 days, with copulations mostly occurring on a single day (Izard et al. 1988). Copulatory plugs are sometimes seen after N. coucang reproduction (Izard et al. 1988). Females of N. pygmaeus and N. coucang solicit copulation by hanging from a branch (often making whistling vocalizations) and copulation occurs thus, with the male grasping both the female and the branch (Zimmermann 1989; Fitch-Snyder & Jurke 2003). N. coucang also solicit copulation by walking in front of the male and urine-marking and vocalizing (Zimmermann 1989). In captivity, N. pygmaeus are seasonal breeders, with most births occurring between January and April. In the wild, they also likely breed seasonally, although the actual timing and duration is unknown (Fitch-Snyder & Jurke 2003). Contrary to this, other species of slow loris are not seasonal breeders, and instead are polyestrous (Fitch-Snyder & Jurke 2003).

Successful reproduction can happen as early as 73 weeks in captive male N. pygmaeus and sexual maturity likely occurs before 14 months of age in males of the species, although actual reproduction usually occurs around 17-20 months old (Weisenseel et al. 1998; Fitch-Snyder & Jurke 2003). Female N. coucang are sexual mature between 17-24 months old (Izard et al. 1988; Weisenseen et al. 1998). Gestation lengths for N. coucang and N. pygmaeus are similar, averaging 191-192.2 days and 188.0 days respectively (Izard et al. 1988; Weisenseel et al. 1998).


N. coucang births are usually singletons, although twinning has been seen (Izard et al. 1988). N. coucang infants are born with open eyes and all of their fur, with gray face, limbs, and ventrum and a brown back with a dark stripe, and can cling to their mothers one hour after birth (Zimmermann 1989; Wiens 2002). Twins are more common in N. pygmaeus than in N. coucang (Fitch-Snyder & Ehrlich 2003). Birth weights in captivity average around 48.2 g (1.7oz), and the interbirth interval is around 16.2 months (Izard et al. 1988). In captivity, N. coucang first groom themselves at four weeks of age, and show first locomotion at around 6.2 weeks old, with drinking, eating and urine marking starting at 9.3, 12.0, and 13.0 weeks respectively (Ehrlich & Macbride 1989). However, in a different captive study, eating of solid food occurred much earlier, and development was described as being extremely quick, with infants showing adult movement and social patterns soon after birth (Zimmermann 1989). Infants are carried by clinging to the mother’s fur on her ventrum, and are almost completely immobile in their first 6-8 weeks of age (Ehrlich 1974; Ehrlich & Macbride 1989). However, in the wild a four-week old infant (N. coucang) was seen to be able to climb about a food tree, albeit not adeptly (Wiens & Zitzmann 2003a). After the first week of life, mothers “park” their infants for prolonged periods, during which, the infants in many cases will not, or are unable to, follow (Ehrlich 1974; Tenaza & Fitch 1984; Ehrlich & Macbride 1989; Wiens 2002; Fitch-Snyder & Ehrlich 2003). From the second week on, infants follow their mothers (Fitch-Snyder & Ehrlich 2003). Wild N. coucang infants will only follow their mothers to a sleeping site (Wiens 2002). Between N. pygmaeus and N. bengalensis, mother-infant pairs of the former spend more time near each other, but overall, there are great similarities in the relationships between mothers and their infants across slow loris species (Fitch-Snyder & Ehrlich 2003). Overall, N. coucang maternal care consists only of suckling, carrying, and grooming (Wiens 2002). Maternal lactation persists around six months and weaning occurs between the fifth and seventh months of age (Izard et al. 1988; Zimmermann 1989).


N. coucang emits eight different types of call used in two basic functional groups, relating to contact or affiliation (including whistles, short keckers), and those relating to aggression and defense (including snarls, grunts, long keckers, and screams) (Zimmermann 1985). Slow lorises do not emit alarm calls (Wiens & Zitzmann 2003b). Whistle calls are often heard from females in estrus (Daschbach et al. 1981). Ultrasonic vocalizations out of the human hearing range, are emitted when slow lorises explore unknown environments and during handling (Zimmermann 1981). Infants emit click sounds when they are isolated from their mother and when they feel distressed (Rassmussen 1986). Click-calls are used as a method for individuals to reconvene at sleeping sites after nightly activity (Wiens & Zitzmann 2003b).


Slow lorises have a gland on their elbows that exude oils used in communication, of which the composition is particular to each species (Hagey et al. 2007). This secretion from the elbow glands probably evolved for communication, but can be toxic to humans if bitten, as licking is one mode for deposition of the scent. This is especially true among people who have had contact with the animals and may have developed allergies to them. Individuals have gone into shock and even died after slow loris bites (Wilde 1972; Hagey et al. 2007).

Olfactory communication is important in slow lorises, and they signal conspecifics by urine marking, and through deposition of scent from glands on their elbows and anus (Tenaza & Fitch 1984; Rasmussen 1986; Hagey et al. 2007). Rhythmic uriniation is one method of scent deposition in the species, in which the animal moves about and deposits urine as it moves (Rassmussen 1986). Facial rubbing on a substrate usually occurs in response to the scent of another slow loris (Rassmussen 1986). Olfactory communication is important in reproduction in slow lorises (Fisher et al. 2003a). N. pygmaeus males overmark the scent-marks of other males. N. pygmaeus urine-marking odor is individually distinguishable among the species, and females use marking and countermarks by males to assess the desirability of the males (Fisher et al. 2003a). Further, in captive experiments, females prefer males whose odor they are familiar with (Fisher et al. 2003b).

Postural and facial communication is not particularly common in slow lorises. However, two commonly seen postures/facial expressions are the grin and bare-teeth displays, both usually accompanied by vocalizations. Grins are shown by infants, usually when stressed. Bare-teeth displays involve showing the teeth, and are seen during agonism, but also during play behaviors (Rassmussen 1986).

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) Behavior . <>. Accessed 2020 July 10.


CITES: Appendix I (What is CITES?)
IUCN Red List: N. javanicus: EN; N. bengalensis, N. pygmaeus, N. coucang coucang, N. coucang menagensis: VU (What is Red List?)
Key: EN = Endangered, VU = Vulnerable, VU = Vulnerable, VU = Vulnerable, VU = Vulnerable
(Click on species name to see IUCN Red List entry, including detailed status assessment information.)


Threat: Human-Induced Habitat Loss and Degradation

Slow loris on branch

Slow lorises are also particularly susceptible to habitat fragmentation and the felling of feed and sleeping trees causes habitat degradation and increased contact with people (Choudhury 2001; Medhi et al. 2004). In India, for example, habitat destruction is the worst threat to slow lorises (Choudhury 1992). Jhum cultivation (slash-and-burn cultivation) is also a significant habitat threat in India, as is tea cultivation and other agricultural land use (Choudhury 1992; Medhi et al. 2004). Often human settlements follow these types of land use, inhibiting secondary growth (Medhi et al. 2004). Other reasons for habitat descrution include monoculture, logging, fuel-wood extraction, land use for paper production, and the construction of infrastructure (Choudhury 1992). In China, habitat destruction is also the biggest threat to resident slow lorises and suitable areas are often destroyed for cash crops such as rubber, sugarcane, and coffee growing (Lan 1999).

Threat: Invasive Alien Species

Due to importation of slow lorises from some areas of their range to others, sometimes non-local species of slow loris (that are not properly identified) are introduced or released if confiscated into habitats in which they are not native, potentially altering the ecology of native species of slow loris (Schulze & Groves 2004).

Threat: Harvesting (hunting/gathering)

Over large areas of their range, slow lorises are collected as pets and for illegal folk medicine. They are one of the most commonly traded protected primates in southeast Asia (Schulze & Groves 2004; Nekaris & Jaffe 2007). In some areas, they are also hunted for meat (Radhakrishna et al. 2006). However, due to their diminutive size, N. pygmaeus are not hunted intensely, but they are probably still sold in markets in Vietnam and even exported (Duckworth 1994; Fitch-Snyder & Thanh 2002). Animals are often exported from their countries of origin for medicinal uses and very often end up in China, but illegal export to Taiwan has also been recorded (Phipps 1992; Fitch-Snyder & Thanh 2002). Even if the lorises are not desired locally, they are often collected in neighboring areas and imported (Schulze & Groves 2004). In China, slow lorises are eaten, the bones are used for medicinal uses, and the fur for local hunting bags (Lan 1999). The illegal trade in the species is further evidenced by slow lorises being found for sale in Indonesian and Cambodian markets. In some areas, the trade is so intense that devoted animal rescue centers are overwhelmed (Malone et al. 2002; Streicher et al. 2002; Nekaris & Jaffe 2007). In Vietnam, collection for medicinal purposes results in captured animals being dried or placed in rice wine (Streicher et al. 2002). Some groups across the broad slow loris range believe that the collection of a loris eyeball may help the person’s eyesight (Medhi et al. 2004). Adding to the threat of their removal from their habitats, slow lorises very often die from the stress of being held captive (Streicher 2004).

Threat: Accidental Mortality

While trying to cross roads, slow lorises are sometimes hit and killed by automobile traffic (Radhakrishna et al. 2006).

Threat: Human Disturbance

In some protected areas of India, armed insurgent groups are present. Such groups may hunt slow lorises, but also discourage the patrols of forest guards, and thus reduce protection afforded to slow lorises (Radhakrishna et al. 2006). Further, recent wars in Indochina have significantly altered or destroyed slow loris habitats (Lan 1999).





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) Conservation . <>. Accessed 2020 July 10.

The following references were used in the writing of this factsheet. To find current references for Nycticebus, search PrimateLit.


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Content last modified: March 18, 2009




Nycticebus coucang
Photo: Andrew Johns
Nycticebus coucang
Photo: J. R. Mackinnon
Nycticebus coucang
Photo: Marilyn Cole
Nycticebus coucang
Photo: Marilyn Cole

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