The Slow Loris Is a Cuddly-looking Primate With a Toxic Bite

By: Patty Rasmussen  | 

Slow loris
The slow loris (Nycticebus bengalensis) has the face of an adorable stuffed animal, but a toxic bite, a trait that's unique among primates and rarely found among mammals. Duke Lemur Center

At first glance, it's easy to believe that the slow loris, a tiny primate with wide, saucer-like eyes is nothing more than a Beanie Boo come to life. But don't let that innocent face fool you. These little creatures prefer their own company, and usually bite when they feel threatened – either from humans or from other slow lorises – raising their arms and licking a highly toxic venom secreted from glands at their upper arm which pools in grooves on their canine teeth. The venom can cause necrosis (death of the tissue) or can even be fatal if not properly treated. In other words, to paraphrase William Shakespeare to our own purposes, "Though the slow loris be but little, it is fierce."

The slow loris was described in 1891 as having the "face of a bear, the hands of a monkey, [and] mov[ing] like a sloth" by American zoologist Dean Conant Worcester. The word "loris" came from the Dutch word "loeris" meaning clown, alluding to the creature's distinctive facial markings. They have small ears on their round, furry heads, with rings around their huge forward-facing eyes (which provide stereo vision). Their eyes have something called the tapedum lucidum – a light-reflecting surface behind the retina that helps them see better in the dark.

Their bodies are solid; they have only the stump of a tail under dense fur. Their weight varies by species – from the Bengal slow loris at 74 ounces (2,100 grams) to the Bornean slow loris at just over 9 ounces (265 grams). Their length, combined head and body, ranges from 7 to 15 inches (18 to 38 centimeters) depending on species.


Slow Lorises Are Nocturnal

Slow lorises are native to Southeast Asia, specifically Vietnam (east of the Mekong River), eastern Cambodia, Laos and the Yunnan province in the south of China. They live in the branches of bamboo and hardwood forests, usually sleeping during the day in crevices or hollows. Lorises are nocturnal, and are considered opportunistic hunters. They use their excellent sense of smell to hunt for insects and other small prey, but will also eat fruit and tree gum (high glucose sap). They lick dew off leaves for moisture.

Slow loris
An adult pygmy slow loris (Nycticebus pygmaeus) nibbling a frozen treat.
Duke Lemur Center

We checked in with researchers at the Duke Lemur Center (DLC) at Duke University in Durham, North Carolina, to find out more about these intriguing critters, although they no longer house lorises at the center. Anna Lee, education technician at the DLC, gives us insight into the slow loris social organization and behavior.

"When two lorises cross paths, interactions are generally positive (i.e., grooming instead of fighting)," she says in an email. "In the wild, males and females will occasionally remain in the same space while their offspring are young, forming small family groups until the offspring get older and disperse. These groups groom each other and sleep in contact with one another, but they frequently forage alone and there doesn't seem to be a clear dominance structure."

Lee's colleague, Jodi Stirk, an animal care technician who worked with the slow lorises when they were at the DLC, says that they exhibited distinctive personalities. "Some are very shy or standoffish, while others are outgoing, curious and interactive with the staff," she says in an email.


They Have Strong Family Bonds

Dr. Anna Nekaris, a professor in primate conservation and anthropology at Oxford Brooks University for 20 years, has studied slow loris in the wild. "They can mate in the wild all year round," she says. "They are amazing families and the offspring can stay with the parents in groups of up to six individuals for up to three years," she says.

That isn't always the case for breeding pairs in captivity, according to Stirk.

"Not all breeding pairs are compatible when they are introduced," she says. "Some pairs are aggressive and can injure each other. Dams (females) are housed with their offspring here until they kick out the youngsters. The age at which a dam evicts her offspring is dependent on that specific female. Some females will tolerate their offspring longer than others and some will kick them out as young as five months."

Lee says it's difficult to find and follow lorises in their remote rainforest habitat. Since they are endangered, Duke researchers were interested in following their life history, studying questions like how long females nurse their young and how long they live in human care.

"Learning how to care for and eventually breed them successfully in human care is important for their continued survival," she says. "All breeding was done at the recommendation of a Species Survival Plan which helps avoid overbreeding and maintains healthy genetics for all slow lorises in human care. While we no longer house them ourselves, what we learned during the years we did keep slow lorises continues to help the colony in human care at other facilities today."

Slow loris
A slender loris (Lemur tardigradus), a species also from the genus Nycticebus and closely related to the slow loris, eating a grape.
Duke Lemur Center

The biggest threats to the survival of slow lorises are two-fold and man-made: the degradation of its habitat and direct human interaction, such as hunting or attempting to domesticate them. Because of these and other threats, all five species of slow loris are listed as either "Vulnerable" or "Endangered" by the International Union for Conservation of Nature (IUCN). The DLC says primates, including slow lorises, don't make good pets and trying to domesticate them is not fair to them. Lorises are meant to live with lorises, not people.

"Slow lorises rely on undisturbed rainforests to live in, something that is in short supply in our ever-changing world," Lee says. "Some are hunted for bushmeat or use in traditional medicines, while other slow lorises are kept as props for tourists or sold into the international pet trade. With their distinctive giant eyes and slow speed, lorises are frequent viral video stars, driving up the practice of keeping them. As always, social media doesn't tell the full story. Lorises taken from the wild frequently have their teeth removed to prevent dangerous bites and their arm-raising behavior seen in videos of 'tickling' is a defensive posture used against threats, like humans."