Are Slow Lorises Venomous? The Science Explained

Slow lorises, the big-eyed primates of South and Southeast Asian forests, are genuinely venomous. That makes them one of very few venomous mammals and the only known venomous primates. Their venom isn’t stored in fangs like a snake’s; the animal has to assemble it from two separate ingredients before it can bite with it.¹ For people, much of the danger from a bite comes from the body’s allergic overreaction rather than from poison alone.²

How a Slow Loris Makes Its Venom

Each slow loris has a small gland on the inside of its upper arm, near the armpit. It oozes an oily, strong-smelling fluid onto the fur. The gland’s tiny ducts open into hair follicles, so the secretion comes out through the skin and coats the hair.³

On its own, that fluid does little. In experiments with mice, the arm-gland fluid alone or saliva alone caused little harm, but the two combined were deadly.⁴ The venom is therefore a two-step system, and the loris activates it by licking the gland and loading its mouth.⁵ When it bites, its sharp lower front teeth carry the mixture into the wound.

A threatened loris raises its arms above its head, which brings the glands toward its mouth. Then it licks or sucks the gland area, blending secretion with saliva. It may hiss and sway while it does this. The raised-arm stance in viral “tickling” videos is this defensive posture; the animal is frightened, and a hand near it is close to a bite.

Unlike a snake, lorises have no fangs or venom ducts in their teeth, and the mixing happens by licking. The teeth themselves aren’t poisonous.

What Is in Slow Loris Venom

The arm gland’s main component is a protein made of two linked chains.⁶ That protein is strikingly similar in structure to Fel d 1, the protein in cat dander that makes people allergic to cats.⁷ In the Javan slow loris, the matching protein shares about half its building blocks with the cat allergen in one chain and about a third in the other.⁸ The immune system may therefore treat loris venom much like cat dander, and people allergic to cats may react to it.⁹ An immune system primed against one protein can react to a look-alike. A cat-allergic person’s antibodies may recognise the loris protein on first contact.

Scientists haven’t yet worked out the full list of compounds in the saliva-gland mixture, and it remains unclear exactly how saliva activates the gland fluid. The toxic effects can’t yet be pinned to a single substance.

What a Slow Loris Bite Does to a Person

Among people who work with lorises and were bitten, nearly 8 in 10 had symptoms afterward.¹⁰ About half rated the pain above 8 out of 10.¹¹ Reported effects included swelling of the face and airway, nausea, headache, tingling or numbness, blood in the urine, tremors and infection.¹² Effects ranged from instant to lasting, with healing taking from one day to over eight months.¹³

Bites serious enough for hospital look different. In 28 people treated in hospital over 11 years, most were bitten on the fingers or hands.¹⁴ 43% developed anaphylaxis, a severe whole-body allergic reaction that can affect breathing and blood pressure.¹⁵ Nearly 3 in 10 went into anaphylactic shock, with dangerously low blood pressure.¹⁶ Wound infection was rare, in only 1 of the 28.¹⁷ These figures describe only the most serious bites that reached hospital, so they don’t tell a traveller the chance that a given bite turns dangerous. Hands are full of nerves, so a bite there can bring lasting numbness or tingling even after the swelling eases.

Reactions can start within minutes. In one reported case, a woman with a cat allergy developed itching, breathing trouble and swollen lips within 2 to 3 minutes of a bite.¹⁸ She reached hospital in shock, with very low blood pressure and a widespread rash.¹⁹ Signs that a bite is turning into a severe allergic reaction include swelling of the lips, tongue or throat; wheezing, shortness of breath or a tight chest; hives or itching spreading beyond the bite; and dizziness or faintness from falling blood pressure.

What to Do If a Slow Loris Bites You

Get away from the animal, then wash the wound well with soap and running water. Stay where help can reach you. If you carry an adrenaline auto-injector for allergies, have it ready, and call emergency services at the first sign of swelling or breathing trouble.

Emergency treatment is the standard allergy treatment. In a reported case of shock after a wild Kayan slow loris bite, the patient received an adrenaline injection into the muscle.²⁰ Doctors then added intravenous steroid and fluids, and blood pressure and oxygen levels recovered within hours.²¹ By the next morning the lip swelling had eased, though a bitten finger was still numb.²² With steroid, antihistamine and antibiotic tablets, the patient was largely back to normal within a week.²³

Adrenaline comes first because it works quickly against the main dangers of a severe allergic reaction, opening the airways and raising blood pressure. It goes into the muscle, usually the outer thigh in auto-injectors, because that route absorbs fast. Steroids and antihistamines act more slowly and are added afterward, so they don’t replace adrenaline in an emergency.

Even a mild-seeming bite deserves a doctor visit. Reactions can build quickly after a calm start. People allergic to cats face higher risk and should mention the allergy. Pain and numbness can persist and need follow-up, and a doctor can advise on any future exposure.

Why Slow Lorises Evolved Venom

Eight years of watching wild Javan slow lorises showed that both males and females use venomous bites to defend territories and mates.²⁴ Across mammals, venom evolved several separate times for purposes such as hunting, defence and mating competition.²⁵ In lorises, one venom appears to serve several jobs at once.²⁶

Parasites are one of those targets. Insects and ticks exposed to the gland-saliva mix were impaired about three-quarters of the time and died about 6 times in 10.²⁷ Lorises smearing it on their fur may protect themselves from ticks that spread disease.²⁸

Venom may also help lorises pass as cobras. Lorises have a dark stripe down the back that becomes longer and darker in seasons when they spend more time on the ground.²⁹ Some scientists think a crouched loris may look like a cobra to predators, warning them off.³⁰ This is still a hypothesis, not proven.

Why Slow Lorises Make Bad Pets

Illegal traders wrongly believe loris teeth are poisonous, so they cut or pull them out.³¹ The venom actually comes from the arm gland and saliva, not the teeth.³² Confiscated lorises often arrive with broken, infected teeth from careless clipping.³³ Traders use nail clippers or pliers, without anaesthetic. Lorises without front teeth usually can’t be returned to the wild.

A clipped loris is still not safe. It still makes venom from its arm gland and saliva, and it can still smear it on its fur, so a person who handles it can react.

Viral videos fuel the trade. International trade in slow lorises is banned under CITES.

Travellers may meet lorises as photo props, and these animals are usually poached and tooth-clipped. Decline the photo and report sellers to local wildlife authorities.