Javan slow loris (Nycticebus javanicus)

Javan slow loris
IUCN Red List species status – Endangered ENDANGERED

Top facts

  • The Javan slow loris is a small, nocturnal primate found only on the Indonesian island of Java.
  • Slow lorises, including the Javan slow loris, are unique among primates in having a venomous bite.
  • Although the Javan slow loris is generally slow moving, it can strike quickly to grab prey.
  • The Javan slow loris is seriously threatened by the illegal pet trade.
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Javan slow loris fact file

Javan slow loris description

GenusNycticebus (1)

Only recently recognised as a distinct species (1) (2) (5) (6), the Javan slow loris (Nycticebus javanicus) is a shy, nocturnal primate with short, woolly fur and only a vestigial tail (7) (8). Slow lorises, including the Javan slow loris, are unique among primates in having a venomous bite (3) (7) (9).

The fur of the Javan slow loris is brown to reddish, with a white or creamy neck and a dark stripe running down the back (2) (6). The underparts of the body are slightly lighter in colour than the upperparts (7) (8). The Javan slow loris has a distinctive facial pattern, with dark lines running from the eyes and ears to the top of the head, creating a white diamond shape on the forehead. The white from this diamond extends onto the snout (2) (6) (7).

Like other slow loris species, the Javan slow loris has a rounded head, and its ears are more or less hidden in its thick fur (7). Its forelimbs and hind limbs are roughly equal in length (7) (10), and the thumb and big toe are perpendicular to the other digits, helping to give the Javan slow loris a powerful grip (7) (8).

The Javan slow loris was previously thought to be a subspecies of the greater slow loris (Nycticebus coucang), but is now considered to be a separate species (1) (2) (11). However, both a short-furred and a long-furred form of Javan slow loris have been recorded (2) (12), and more research may be needed into this species’ taxonomy to determine whether these are two distinct types (1).

Slow loris species have been reported to give a low, buzzing hiss or growl when disturbed, and may also produce high-pitched contact calls and whistles (7) (8).

Nycticebus coucang, Nycticebus coucang javanicus, Nycticebus ornatus.
Average head-body length: 29 cm (2)
750 - 1,150 g (3)

Javan slow loris biology

The Javan slow loris is active at night (1) (5) (8) (9) and sleeps in tree hollows or vegetation during the day (8) (10) (12). As its name suggests, this species moves with quite slow, deliberate movements as it walks or climbs hand-over-hand along branches (7) (8) (10).

The diet of the Javan slow loris is quite varied, and includes sap, flowers, fruit, insects, bird eggs and even small vertebrates, such as lizards and small mammals (5) (7) (8) (10) (12) (13). Like other slow lorises, the Javan slow loris is also able to gouge trees with its teeth to feed on gum (10) (12) (13). Despite its slow, stealthy movements, this species can strike quickly to seize prey with its hands (7) (8) (9) (13).

The Javan slow loris is usually seen alone or in pairs (7) (12), but has also been known to sleep in small groups (12). In general, slow lorises are not thought to have a distinct breeding season, and births may occur throughout the year. Male slow lorises are territorial, and do not tolerate the presence of other adult males in their territory (7) (8).

Little specific information is available on the breeding behaviour of the Javan slow loris, but it is likely to be similar to that of other slow loris species. In general, female slow lorises give birth to a single infant after a gestation period of just over six months (8). Both the male and female may take turns at carrying the infant, or it may be left clinging to a branch for short periods while the adults forage (7) (8). Young slow lorises are weaned at about 5 to 7 months old, and reach sexual maturity at around 17 to 24 months. Slow lorises have been known to live for over 26 years in captivity (8).

The only venomous primates, slow lorises produce venom by combining secretions from a gland on the elbow with saliva (3) (7). The exact function of the venom is not known, but it is likely to be involved in protection against predators (3). Adult slow lorises may lick their young to spread the venom over them, possibly to protect them (7), and when threatened a slow loris often covers its head with its arms, allowing it to take in the toxin from its elbow glands (9). The bite of a slow loris can be very painful, and can potentially cause serious allergic reactions in humans (3) (7) (9).


Javan slow loris range

As its common name suggests, the Javan slow loris is found only on the Indonesian island of Java (1) (5) (6), where it is known to occur in western and central regions (1) (5). This species is thought to occur at elevations from sea level to around 1,600 metres, but is more common at higher elevations (1) (5).


Javan slow loris habitat

The Javan slow loris has been found in both primary and secondary forest (1) (5) (12), including bamboo forest, mangroves and plantations (12). An arboreal primate, it needs connections between trees, such as those provided by vines, to be able to move around the forest (1) (5).


Javan slow loris status

The Javan slow loris is classified as Endangered (EN) on the IUCN Red List (1) and is listed on Appendix I of CITES (4).

IUCN Red List species status – Endangered


Javan slow loris threats

Its large eyes and cute appearance make the Javan slow loris popular in the pet trade, and illegal trade is still the most significant threat to this small primate, despite national and international protection (1) (3) (5) (6) (9) (14). The number of Javan slow lorises sold in markets is too high for the wild population to be able to recover, particularly given this species’ low reproductive rate (5) (6) (15).

Due to their venomous bite, many captive slow lorises have their front teeth removed, often resulting in infection, malnutrition or death. This cruel practice also means that any confiscated individuals are unlikely to survive if returned to the wild (3) (5) (6) (14). Attempted reintroductions can also cause problems if the wrong species are returned to the wrong areas, potentially leading to hybridisation between different species whose ranges do not normally overlap (2) (6).

The Javan slow loris is also captured for use in traditional medicine (1) (3) (5) (6) (9) (14), and is sometimes taken for use as a photographer’s prop (3). Unfortunately, this slow-moving primate is easy to catch, particularly as it often sleeps on exposed branches, is easily dazzled by bright lights, and instinctively clings to branches rather than fleeing (1) (3) (6). The Javan slow loris is often captured opportunistically by local people during forest clearance (1) (5) (6).

A further threat to the Javan slow loris comes from habitat loss (1) (3) (5) (6). Less than 10 percent of Java’s original forest remains, and only an estimated 20 percent of suitable Javan slow loris habitat is still intact. Roads and human disturbance also negatively affect this species (5) (6).

The combined threats of hunting and habitat loss mean that the Javan slow loris is now considered to be one of the world’s most endangered primate species (5) (6). Its exact population size is unknown, but this species has been recorded at very low densities in the wild (1) (5).


Javan slow loris conservation

The Javan slow loris is protected under Indonesian law (1) (2), and is also listed on Appendix I of the Convention on International Trade in Endangered Species (CITES), making international commercial trade in this primate illegal (4). Although the Javan slow loris occurs in a number of protected areas (1) (11), only around 17 percent of its potential distribution is protected (5) (6), and its status in some reserves is uncertain (1).

Small populations of confiscated Javan slow lorises occur in rescue centres, but mortality is often high due to dental infections or improper care (5) (6). Fortunately, this is being improved with a specialised facility set up by International Animal Rescue Indonesia, which cares for and rehabilitates confiscated slow lorises and, where possible, reintroduces them to the wild (6) (9) (14). Animals that are released are being fitted with radio collars so they can be followed and studied (9) (14). The Little Fireface Project, named after the Sudanese word for loris, is also working to conserve slow loris species, through research, education, workshops and media campaigns (3).

Other recommended conservation measures for the Javan slow loris include producing improved field guides, allowing this and other Southeast Asian primates to be properly identified (1). Increased protection of Javan slow loris habitat is also needed (6), as is further education work, and more studies of this enigmatic primate in the wild (6) (14).

View information on this species at the UNEP World Conservation Monitoring Centre.

Find out more

Find out more about slow lorises and their conservation:

More information on conservation in Indonesia:



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An animal which lives or spends a large amount of time in trees.
The state of being pregnant; the period from conception to birth.
An organ that makes and secretes substances used by the body.
Cross-breeding between two different species or subspecies.
Active at night.
Primary forest
Forest that has remained undisturbed for a long time and has reached a mature condition.
Secondary forest
Forest that has re-grown after a major disturbance, such as fire or timber harvest, but has not yet reached the mature state of primary forest.
A population usually restricted to a geographical area that differs from other populations of the same species, but not to the extent of being classified as a separate species.
The science of classifying organisms, grouping together animals which share common features and are thought to have a common ancestor.
Describes an animal, a pair of animals or a colony that occupies and defends an area.
An area occupied and defended by an animal, a pair of animals or a colony.
Animals with a backbone, including mammals, birds, reptiles, amphibians and fish.
Describing a structure or organ that has diminished in size, through evolution, to the point where it no longer functions. Only traces may remain.


  1. IUCN Red List (May, 2013)
  2. Nekaris, K.A.I. and Jaffe, S. (2007) Unexpected diversity of slow lorises (Nycticebus spp.) within the Javan pet trade: implications for slow loris taxonomy. Contributions to Zoology, 76(3): 187-196.
  3. The Little Fireface Project (May, 2013)
  4. CITES (April, 2013)
  5. Mittermeier, R.A. et al. (2012) Primates in Peril: The World’s 25 Most Endangered Primates 2012-2014. IUCN/SSC Primate Specialist Group, International Primatological Society, Conservation International, and Bristol Conservation and Science Foundation, Bristol, UK. Available at:
  6. Mittermeier, R.A. et al. (2009) Primates in Peril: The World’s 25 Most Endangered Primates 2008-2010. IUCN/SSC Primate Specialist Group, International Primatological Society, and Conservation International, Arlington, Virginia. Available at:
  7. Ankel-Simons, F. (2007) Primate Anatomy: An Introduction. Academic Press, San Diego, California.
  8. Nowak, R.M. (1991) Walker’s Mammals of the World. The Johns Hopkins University Press, Baltimore and London.
  9. International Animal Rescue - Saving the slow loris (May, 2013)
  10. Fleagle, J.G. (2013) Primate Adaptation and Evolution. Third Edition. Academic Press, San Diego.
  11. Nekaris, K.A.I., Blackham, G.V. and Nijman, V. (2008) Conservation implications of low encounter rates of five nocturnal primate species (Nycticebus spp.) in Asia. Biodiversity and Conservation, 17: 733-747.
  12. Nekaris, K.A.I. and Munds, R. (2010). Using facial markings to unmask diversity: the slow lorises (Primates: Lorisidae: Nycticebus spp.) of Indonesia. In: Gursky-Doyen, S. and Supriatna, J. (Eds.) Indonesian Primates. Springer, New York.
  13. Streicher, U., Wilson, A., Collins, R.L. and Nekaris, K.A.I. (2013) Exudates and animal prey characterize slow loris (Nycticebus pygmaeus, N. coucang and N. javanicus) diet in captivity and after release into the wild. In: Masters, J., Gamba, M. and Génin, F. (Eds.) Leaping Ahead: Advances in Prosimian Biology. Springer, New York.
  14. People’s Trust for Endangered Species (PTES) - Stopping the trade in Javan slow lorises (May, 2013)
  15. Nekaris, K.A.I. and Nijman, V. (2007) CITES proposal highlights rarity of Asian nocturnal primates (Lorisidae: Nycticebus). Folia Primatologica, 78: 211-214.

Image credit

Javan slow loris  
Javan slow loris

© Zulham Advan

Zulham Advan


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