BENGAL SLOW LORIS

Nycticebus bengalensis

Geographic Distribution and Habitat
The Bengal slow loris is a native of southeastern Asia, residing in the countries of Bangladesh, Cambodia, Vietnam, Lao People’s Democratic Republic, Thailand, Myanmar (formerly Burma), northeastern India, and southern China. Of all the loris species, the Bengal slow loris occupies the greatest and northernmost range, with the largest populations living in eastern Thailand.

These prosimians (the oldest, most “primitive” order of primates) are typically found in tropical, subtropical, evergreen, and semi-evergreen forests. They prefer dense canopy cover, where they can hide from predators, but Bengal slow lorises can also be found at forest edges where insect prey is more plentiful. Unfortunately, with humans increasingly destroying their habitat for agricultural use, Bengal slow lorises are being forced to live in patches of scrub forest.

TAXONOMIC NOTE

Previously classified as a subspecies of the Sunda Slow Loris, aka Greater Slow Loris (Nycticebus coucang), the Bengal slow loris was recognized as a distinct species in 2001.

Bengal Slow Loris geographic distribution. Map: IUCN, 2020

Size, Weight, and Lifespan
As the largest of the slow loris species, the Bengal slow loris is three times the size of the smallest loris, the pygmy slow loris (Nycticebus pygmaeus).

Head-to-body length for the Bengal slow loris is 10 to 15 in (26 to 38 cm), and the primate weighs up to 4.4 lb (2 kg).

Males and females are relatively the same size and look alike. The only way to tell them apart is by their genital distinction. Otherwise, the species exhibits no sexual dimorphism (the different physical characteristics between males and females of a species).

Lifespan in the wild is about 15 years, assuming the Bengal slow loris’s life is not cut short due to hunting or habitat loss.

Appearance
Interwoven in the plush coat of the Bengal slow loris are distinct color patterns that allow this primate to be identified from other slow loris species. Pelage coloring is brown-gray on the upper body with a dramatic dark stripe down the center of the back, and their underparts are white. Tiny ears sit atop a round head that is covered by a white “cap.”  

The loris’s facial features are defined by large, forward-facing eyes that reflect a dramatic, orange-red “eye shine.” Arched “eyebrows” in the brown fur pattern encircling each eye conspire to evoke an expression of mild surprise. A narrow white strip of fur separates the eyes and extends to a short, faintly pink snout.

Bengal slow lorises have needle-like teeth with tilted incisors that form a tooth comb (or dental comb), shaped like a garden spade at the front of their mouth on the lower jaw.

Hands are fitted with opposable thumbs that are widely separated from four fingers. Evolution has rendered the tail of the Bengal slow loris nonfunctional, a barely noticeable vestigial appendage

What Does It Mean?

Anaphylactic shock:
A potentially life-threatening response characterized by a sudden drop in blood pressure, rapid swelling in the throat, acute respiratory distress, and collapse of circulation.

Exudate:
A substance, such as gum, sap, or resin, which flows from the vascular system of a plant.

Lothario: 
A man whose chief interest is seducing women.

Pelage: 
The fur, hair, or wool of a mammal.

Vestigial: 
A part of the body that in the course of evolution, has degenerated and become functionless; the last small part that remains of something that once existed.

Visit the Glossary for more definitions

Diet
The Bengal slow loris’s menu consists of plant exudates along with nectars, fruits, tree bark, insects, and bird eggs. Their favorite meals, however, are the resins and gums of six species of plants that make up 94 percent of their winter diet and 67 percent of their summer diet. These plant species include the flowering Bauhinia, liana vines, and flowering Terminalia trees. Nectar is their second-favorite food, making up 22 percent of their summer diet.

Daily Life and Group Dynamics
Active during nighttime hours (making them nocturnal), Bengal slow lorises spend most of their time in trees (making them arboreal), moving through the forest quadrupedally (on all fours) with deliberate movements as they forage. Their hands are supremely adapted to climbing, thanks to their opposable thumbs and fingers which, when clenched together, allow them a pincer-like grip (like a crab, lobster, or scorpion!). And those big, alluring eyes aren’t just for looks. Each is endowed with stereoscopic vision; that is, each eye sees a slightly different image of a single perception. Their specialized eyesight gives them an increased awareness of objects through greater depth perception and enhanced “night vision.” To get to the gum, resin, and other cellular fiber found in tree bark, lorises use their incisor teeth to gouge or scrape holes in the bark. Their long, narrow tongues help them to scoop these exudates into their mouth.

Although some Bengal slow lorises are solitary individuals, most live in family groups. No dominance hierarchy exists; they live peaceably with one another and are tolerant of other loris species. Home ranges overlap and vary in size, influenced by the number of competitors for food sources and by habitat quality. Each night, Bengal slow lorsises travel, either alone or in pairs, between 66 and 98 ft (20 to 30 m) to forage. Bengal slow lorises have been observed foraging with pygmy slow lorises. 

A common practice for mothers is to “park” their infants on a tree limb, camouflaged by dense vegetation, while they go off to forage. 

Daytime is meant for snoozing, curled up into a ball. Tree holes and dense vegetation provide the species’ sleeping quarters, which Bengal slow lorises sometimes share with other loris species.

NOT-SO-Fun Facts

Tickling is Torture!

Videos, memes, and images of pet slow lorises have become increasingly popular on the Internet, leading to more people who want a slow loris as a pet.

These “cute” videos most often feature a slow loris who is being tickled by a human. With his head bowed and his little arms stretched above his head as he endures this activity, the primate might look adorable to you. But the sad truth is that the loris is in great distress—he is being caused to suffer.

If the loris were in the wild, the primate would assume this defensive posture to release the toxic secretion (exudate) from its brachial gland. But as he is maimed, he has no defense, and is completely vulnerable—a pitiful state that aligns with the Bengal slow loris’s conservation status.

Don’t contribute to the lorises’ suffering! Instead of sharing these “tickling” videos, help spread your newfound knowledge about lorises to your friends and help save the species!

Daily Life and Group Dynamics
Active during nighttime hours (making them nocturnal), Bengal slow lorises spend most of their time in trees (making them arboreal), moving through the forest quadrupedally (on all fours) with deliberate movements as they forage. Their hands are supremely adapted to climbing, thanks to their opposable thumbs and fingers which, when clenched together, allow them a pincer-like grip (like a crab, lobster, or scorpion!). And those big, alluring eyes aren’t just for looks. Each is endowed with stereoscopic vision; that is, each eye sees a slightly different image of a single perception. Their specialized eyesight gives them an increased awareness of objects through greater depth perception and enhanced “night vision.” To get to the gum, resin, and other cellular fiber found in tree bark, lorises use their incisor teeth to gouge or scrape holes in the bark. Their long, narrow tongues help them to scoop these exudates into their mouth.

Although some Bengal slow lorises are solitary individuals, most live in family groups. No dominance hierarchy exists; they live peaceably with one another and are tolerant of other loris species. Home ranges overlap and vary in size, influenced by the number of competitors for food sources and by habitat quality. Each night, Bengal slow lorsises travel, either alone or in pairs, between 66 and 98 ft (20 to 30 m) to forage. Bengal slow lorises have been observed foraging with pygmy slow lorises. 

A common practice for mothers is to “park” their infants on a tree limb, camouflaged by dense vegetation, while they go off to forage. 

Daytime is meant for snoozing, curled up into a ball. Tree holes and dense vegetation provide the species’ sleeping quarters, which Bengal slow lorises sometimes share with other loris species.

Specialized Defense Mechanism
To further ensure the safety of their young from predators, in addition to using camouflage, mothers will coat their babies with secretions (exudates) from scent glands (known as brachial glands) that are located on the inside of their elbows. When combined with saliva, these secretions become toxic. So if a predator, such as a python, decides to make an appetizer out of a protectively coated infant, the vile taste of the protective secretions will produce an unpleasant physical reaction to the would-be predator. (Think of putting a spoiled piece of food into your mouth that you immediately spit out!)

Both male and female Bengal slow lorises make use of these specialized defense mechanisms when threatened by a predator. After rolling themselves into a protective posture with their heads bowed downward and their arms over their heads, they activate their brachial glands and coat their heads with the foul-tasting secretions—giving would-be predators second thoughts.

Bite me! Bengal slow lorises will also bite, if they must, to defend themselves. Their toxin is secreted in their sweat, so when they lick their brachial glands, the toxin mixes with their saliva as these primates deliver a painful bite with their comb-like teeth. But it may be a point of scientific dispute as to whether their sharp incisors act as conduits for “channeling” and injecting this toxin into their bite victim’s flesh. While earlier research seemed to support this theory, more current research disagrees, instead stating that the dental comb plays no direct role as conduit for injecting the toxins.

Additional irritants are also released through the brachial gland exudates, causing ill-effects in would-be predators. These secretions might serve an anti-parasitic role. Compared to other primates, who are often ridden with fleas, lorises have an extremely low occurrence and intensity of parasite infestation.

Captive Bengal slow lorises, victims of the illegal pet trade industry, will also bite. Humans who have been bitten by their exotic pet have reported painful reactions, including mild cases of anaphylactic shock. But these bite injuries are related to the loris’s sharp, pointed teeth, and not to its toxins.

Nevertheless, to mitigate this danger, Bengal slow loris pets are routinely maimed; that is, their teeth and protective elbow patches are forcibly removed.

Milder allergic reactions to loris bites are also possible, similar to those induced in individuals who are hypersensitive cat dander.

Bengal slow lorises use their dental combs to groom one another, a tactile activity that helps to strengthen social bonds. Playtime, particularly between mothers and their babies, also reinforces social bonds.

Communication
Bengal slow lorises use a variety of vocalizations to communicate with one another. Infants use “chitters” and “clicks” to get their mother’s attention or to call her to their parked location if she is out foraging. Upon hearing her infant’s call, a mother will immediately return.

High-pitches whistles are used to attract a mate. When she is in estrus (sexually receptive) a female will supplement her whistling by scent-marking a spot with her urine, to increase her chances of luring a male.

Like most nocturnal primates, Bengal slow lorises rely on olfactory cues. Scientists posit that brachial gland secretions might be used to mark home ranges, to deter predators, or warn other lorises of potential danger.

Bengal slow lorises use their dental combs to groom on another, a tactile activity that helps to strengthen social bonds. Playtime, particularly between mothers and their babies, also reinforces social bonds.

Reproduction and Family
Not a lot of information specific to Bengal slow loris reproduction is known, so some conclusions are drawn from the reproductive biology of other slow loris species.

After she whistles and scent marks with her urine, a female loris will gauge a potential male suitor’s interest by cocking her head to look back at him. If he is interested, he will respond by sniffing the female’s urine mark, and if he likes her scent, he will add his own urine mark on top. Then he will return her whistle and approach. Dropping below a branch, the female assumes a posture that is an invitation to copulate, and the two will mate. Social grooming or play may follow (no rolling over and going to sleep for Romeo).

A female slow loris will mate with multiple males during the time that she is receptive (roughly, a 37 to 54-day period); males may also mate with multiple females. Slow lorises mate throughout the year.

Males and females reach sexual maturity between 1 to 1.5 years of age; however, they do not successfully conceive as soon as they are sexually mature. Males are just over 4 years old when they successfully sire their first progeny. Females are generally just over 3 years old.

After a gestation period of 6 to 7 months, a female slow loris typically gives birth to a single infant. Occasionally, twins have been reported.

Female slow lorises breed every two years; scientists believe this interval allows for the intense maternal care that mothers provide to their young. The powerful bond between mother and infant begins at birth and often lasts a lifetime.

Infants are born with their eyes open, and their bodies are covered with fur. Slow loris infants are able to feed themselves almost immediately (this advanced state of being at birth is scientifically described as “precocial”). Their brachial glands become active at 6 weeks of age.

Infants ride on their mother’s backs for up to 3 months. When they are a few months old, young slow lorises spend a lot of time play-wrestling with their mothers and with other adults in the group. Fathers, however, do not contribute to parental care; after impregnating the female, he goes from Romeo to Lothario—even if the female was the seducer!

The earliest that slow loris infants are considered weaned is age 6 months, but mothers continue to nurse their infants until they reach sexual maturity. Young slow lorises are considered independent between the ages of 6 and 18 months. 

Ecological Role
By feeding on the nectar of multiple flowers, Bengal slow lorises act as pollinators as they help to regenerate plant life throughout their habitat’s ecosystem.

Conservation Status and Threats
The Bengal slow loris is listed as Endangered by the International Union for Conservation of Nature (IUCN, 2015), appearing on the IUCN Red List of Threatened Species as a result of a combination of habitat loss and severe pressures from hunting which have caused a greater than 50% reduction in their population over three generations (approximately 24 years). The species is also predicted to decline by more than 50% over the next three generations across its entire range due to continuing hunting pressures and loss of habitat.

Hunted animals are used for traditional medicines, and for national and international trade in pets and tourist photo props. Bengal slow lorises are also hunted for meat, and their body parts are used as tourist key rings. The combined effects of forest loss of more than 30% over the last 24 years, and disappearance of the species in several locations in countries like Cambodia due to hunting, and continued threats into the future are factors determining the declines in the past, continuing, and suspected declines in the future.

Their hillside forests are deliberately burnt to the ground to create agricultural tracts of land. The increase in roads has led to the deaths of numerous loris individuals, who have been struck and killed by vehicles. Hunting for bushmeat and for folkloric medicine have also taken a toll on the Bengal slow loris.

But the illegal exotic pet trade industry may pose the most heinous threat against the species. Commonly found in homes throughout southern Asia, this prosimian with the big eyes is routinely captured to become a household pet. Using pliers or wire cutters and administering no anesthesia to lessen the pain, kidnappers rip out the lorises’ front teeth and remove their protective elbow patches. The maimed animals are then shoved into tiny cages for display at Indonesian markets, where the lorises are sold locally for as little as $20 (as reported by an article in Scientific American). At the other end of this illegal pet trade spectrum is the exorbitant export price tag of $6,000 per loris headed to Japan (as reported in a study of Vietnam’s Bengal slow loris population, conducted by the Center for Biodiversity and Conservation). The species is also a popular export pet to Russia.

Many of these kidnapped lorises die of infection shortly after being sold. The removal of their teeth hampers their ability to eat, and their normal sleep patterns are turned upside down, with their human owners attempting to play with these nocturnal creatures during the daytime.

Known predators to this species in the wild are pythons, hawk eagles, and orangutans.

Conservation Efforts
The Bengal slow loris is listed in Appendix I of the Convention on International Trade in Endangered Species (CITES), an international agreement between governments whose goal is to ensure that international trade in specimens of wild animals and plants does not threaten their survival. Additionally, each of the species’ host countries has enacted specific wildlife protections, with Vietnam including the Bengal slow loris under its highest wildlife protection legislation—even recognizing the Bengal slow loris on a postage stamp.

However, as is often the case with endangered species, laws created to protect them are largely ignored and difficult to enforce.

The San Diego Zoo has published slow lorises husbandry manuals, promoted public awareness, conducted field surveys, and supported slow loris rescue facilities. The last captive slow loris birth at the San Diego Zoo was in 2001. According to the International Species Information System, a non-profit organization affiliated with zoos worldwide, however, slow loris species do not fare well in zoos.

Groups dedicated to protecting the Bengal slow loris include:

  • Bangladesh Slow Loris Research and Conservation Project, initiated to collect comprehensive data on the Bengal Slow Loris to increase knowledge of the species and help in conservation. Presently, the organization is working in Satchari National Park, Sylhet Division, close to the border of India.
  • Love Wildlife Foundation of Thailand encourages the conservation of the slow loris through education programs, school talks, and Youth Ecological Network (YEN) as well as awareness campaigns to educate and inform the general public of their plight.
  • The foundation also works together with the Thai Department of National Parks, Wildlife and Plant Conservation (DNP) to help keep slow lorises free in their natural homes and optimize the well-being of captive/confiscated ones.
  • International Animal Rescue (IAR) operates sanctuaries that provide lifelong care to slow lorises who have had their teeth removed, while also providing education and awareness programs to local people to help end domestic trade. By collaborating with authorities, healthy slow lorises are released back into the wild.
  • Center for Biodiversity and Conservation. Director of Biodiversity Informatics Research, Mary Blair, says that “rigorous science” is necessary for a conservation action plan. A study conducted in Vietnam was funded by the Center for Biodiversity and Conservation at the American Museum of Natural History, the National Science Foundation, the Margot Marsh Biodiversity Foundation, the Eppley Foundation of Research, Disney Worldwide Conservation Fund, and the USAAID Peer Science Program. 

References:

  • http://www.arkive.org/bengal-slow-loris/nycticebus-bengalensis
  • http://animaldiversity.org/accounts/Nycticebus_bengalensis
  • http://www.iucnredlist.org/details/39758/0
  • http://www.ourendangeredworld.com/species/land-mammals/bengal-slow-loris
  • http://pin.primate.wisc.edu/factsheets/entry/slow_loris/taxon
  • http://www.brookes.ac.uk/microsites/the-slow-loris/slow-loris-facts
  • https://primatology.net/2010/10/19/are-slow-lorises-really-venomous
  • https://en.wikipedia.org/wiki/Bengal_slow_loris
  • https://en.wikipedia.org/wiki/Conservation_of_slow_lorises
  • http://www.huffingtonpost.com/2015/06/17/slow-loris-videos_n_7606524/
  • https://www.karger.com/article/FullText/444231
  • https://www.internationalanimalrescue.org/truth-behind-slow-loris-pet-trade?currency=USD
  • https://www.youtube.com/watch?v=An5wNXzmz5E
  • https://blogs.scientificamerican.com/extinction-countdown/new-slow-loris-discovered-venomous-primates
  • https://www.youtube.com/watch?v=EXR1X83uFfs
  • http://www.eprc.asia/our-animals/lorises/bengal-slow-loris
  • http://lemur.duke.edu/discover/meet-the-lemurs/slow-loris
  • https://www.youtube.com/watch?v=JLI7Qoh-cYo​

Written by Kathleen Downey, August 2017. Conservation status updated July 2020.