Are slow lorises really venomous?

Slow loris by Frans Lanting. Photo from The Guardian.

I must say, the idea of venomous primates never crossed my mind. While venomous species do exist in mammals, it is much more common in insects, reptiles and fishes. In primates, slow lorises (genus Nycticebus) are though to be venomous in Thai folklore (Wilde, 1972) but are they really?

As of 2010, the genus Nycticebus consists of four species: Pygmy slow loris (Nycticebus pygmaeus), Javan slow loris (Nycticebus javanicus), Sunda slow loris (Nycticebus coucang) and Bengal slow loris (Nycticebus bengalensis). The Javan slow loris was previously recognized as a subspecies but has since been elevated to species status. These prosimians are found in different parts of Southeast Asia. Nycticebus range, in red. Illustration from Primate Info Net.

Slow lorises are arboreal primates that move quadrupedally between branches. They are nocturnal and omnivorous, feeding on plant matter and insects. Slow lorises sleep during the day, curled up like a ball in hidden parts of trees above ground. Their predators include pythons (Python reticulatus), hawk-eagles (Spizaetus cirrhatus) and orangutans (Pongo pygmaeus). Slow lorises have a relatively low metabolism compared to similar-sized mammals (Gron, 2009). Sunda slow loris (Nycticebus coucang). Photo from Primate Info Net.

Colors and markings in Nycticebus species and subspecies. Illustration from Loris Conservation.
Venomous vs. Poisonous

Although the words “venomous” and “poisonous” are used interchangeably in everyday speech, they are actually fundamentally different. By definition, venom has to be injected into the body, introduced by a bite or a sting. Poison, on the other hand, is ingested or inhaled  into the body by the victim. Thus, venomous and poisonous animals are altogether different.

The blue dart frog (Dendrobates azureus) is a poisonous animal while the Indian cobra (Naja naja) is a venomous animal.
Brachial gland of slow lorises
The flexor surface or the ventral side of the elbow has a slightly raised but barely visible swelling termed the brachial gland (Hagey et al., 2006; Krane et al., 2003). Observations from captive slow lorises show that when the animal is disturbed during handling, they secrete about 10 microliters (μL) of clear, strong-smelling fluid in the form of an apocrine sweat (exudate) from their brachial gland . Usually, male and female slow lorises assume a defensive stance when disturbed. They bend their heads downwards between uplifted forelegs, rubbing the brachial gland exudate onto their head and neck. Slow lorises frequently lick their own brachial gland regions and also wipe their brachial gland against their head. The brachial gland is active in lorises as young as 6 weeks old (Hagey et al., 2006). Illustration shows the brachial gland (dark patch) on the ventral side of a slow loris. Drawing by Helga Schulze (Krane et al., 2003).

Brachial gland exudate and Fel d 1

The brachial gland produces exudate with an allergen that is similar to the Fel d 1 cat allergen (Hagey et al., 2006; Krane et al., 2003). This brachial gland exudate shares a high degree of similarity in sequence, as well as unusual disulfide-bridged heterodimeric structure similar with Fel d 1. Fel d 1 is an allergen found mostly in saliva and the sebaceous glands (glands found inside the skin) of domestic cats, Felis catus. Humans with a cat allergy are allergic to five known allergen produced by domestic cats, Fel d 1 being one of them. However, the biological function of Fel d 1 is still currently unknown (Grönlund et al., 2010).

So are slow lorises venomous or poisonous?
To answer this, let’s revisit the definitions of venomous and poisonous. A venomous animal injects toxins into its victim’s body by bite or sting. A poisonous animal, on the other hand, produces toxins that are poisonous once inhaled or ingested. Medical literature shows that human – slow loris injuries come from slow loris bites and not from ingesting their toxins. So are slow lorises venomous? Well, not quite.

Slow lorises have needle-like teeth called dental combs or tooth combs on their lower jaw. Paired with the constant licking of the brachial gland, it is not surprising that one would assume the dental comb plays a part in injecting brachial gland exudate into unsuspecting victims (Hagey et al., 2006). However, this is not the case.

Used for grooming, dental combs might look menacing to some but their function is less sinister than one might conjure up. A bite from a slow loris is painful due to their sharp pointed teeth. Illustration of slow loris teeth from Loris Conservation. The dental comb is on the lower jaw, shape like a spade.

Wilde (1972) reports that the victim of a slow loris bite immediately succumbs to anaphylactic shock (extreme allergic reaction) followed by hematuria. In spite of that, the victim fully recovered. There is no clinical evidence of toxic substances in slow loris saliva to support the notion that they are venomous (Wilde, 1972).

Another incident involves a 34 year-old woman who is 19 weeks pregnant. She was bitten by a pygmy slow loris at the zoo she works in. The patient only complained about an acute pain at the location where she was bitten. She did not go into anaphylactic shock (Kalimullah et al., 2008).

Slow loris bite. Photo by Helena Fitch-Snyder from Loris Conservation.

Reports of slow loris bites are rare in literature. However, based on these published reports, it seems that slow loris bites are not venomous (Kalimullah et al., 2008; Wilde, 1972). Due to the high degree of similarity between the brachial gland exudate of slow lorises and the Fel d 1 allergen in domestic cats, the anaphylactic shock expressed by victims is probably just a reaction to the exudate’s allergen.

What is the function of the brachial gland exudate?

Hagey et al. (2007) posit that the brachial gland exudate is used as olfactory signalling to broadcast individual home range and territories. Most nocturnal primates rely on olfaction — slow loris included. Since brachial gland exudates are not an immediate response to stress or pursuit, their function might be to deter predators, warn other slow lorises of danger or even both (Hagey et al., 2006).

I’m looking forward to more studies on these prosimians and the properties of their brachial gland exudates. More research, as well as slow loris bite records, are needed to elucidate the effects of brachial gland exudates on humans.

Gron, KJ. 2009. Primate Factsheets: Slow Loris (Nycticebus) Taxonomy, Morphology & Ecology.Primate Info NetRetrieved October, 19 2010

Grönlund, H. Saarne, T. Gafvelin, G. van Hage, M. 2010. The Major Cat Allergen, Fel d 1, in Diagnosis and Therapy. International Archives of Allergy and Immunology 151(4): 265-274.

Hagey, LR. Fry, BG. Fitch-Snyder, H. 2007. Talking Defensively: A Dual Use for the Brachial Gland Exudate of Slow and Pygmy Lorises. Primate Anti-Predatory Strategies 2: 253-272 DOI: 10.1007/978-0-387-34810-0_12.

Krane, S. Itagaki, Y. Nakanishi, K. Weldon, PJ. 2003. “Venom” of the slow loris: sequence similarity of prosimian skin gland protein and Fel d 1 cat allergen. Naturwissenschaften 90: 60-62.

Kalimullah, EA. Schmidt, SM. Schmidt, MJ. Lu, JJ. 2008. Beware the Pygmy Slow Loris? Clinical Toxicology 46(7): 602.

Wilde, H. 1972. Anaphylactic Shock Following Bite by a ‘Slow Loris’, Nycticebus coucang. The American Journal of Tropical Medicine and Hygiene 21(5): 592-594.

Originally posted on The Prancing Papio.

20 thoughts on “Are slow lorises really venomous?

  1. This is extremely interesting … It seems that there are still many things we ignore on basic primate biology … Now the question: do you think this is an “adaptation”? I mean, is this a specific defense directly selected for fitness advantage, or simply a “secondary consequences of biochemical incompatibility”?

    1. You’re right Emi. There are still a lot we don’t know about primate biology and physiology, especially nocturnal ones. I think it’s secondary consequence, much like the cat allergen. However, since most people don’t know about the reaction, they probably think that slow lorises are poisonous. They are as poisonous as a cat, really.

  2. This seems like a well thought out and researched piece. Just technical enough to be over my head at times, but simple enough to convey the point easily. Interesting subject.

  3. Thanks Steven! Glad you liked it. I wrote this after hearing a conversation at the zoo I volunteered in. I was pretty shocked at first to hear about a poisonous primate so I looked into it and decided to share what I found.

  4. Brilliant article, nice work! I wrote a bit about the alleged venomosity of slow lorises when covering slender lorises in August 2010 (here on Tetrapod Zoology), but am pleased to say that I didn’t make any bold or silly claims about full-fledged venom production.

  5. Very interesting…I was bitten out in Thailand by a (very cute) slow loris but thought it was a monkey. Put me in hospital 6 months later….by the way I’m not allergic to cats.

    1. It probably was not anything to do with the slow loris but the fact that you received an open wound in Thailand. Any country that isn’t yours has to many different kinds of bacteria and viruses to qualify that the slow loris was the cause of your hospitalization.

      to the author of this article, I appreciate your research and wish that you spread your findings because I believe that domesticating this animal will save them from an inevitable extinction. Unfortunately, there are a plethora of reasons why to not domesticate this animal, a big one being the assumption that it is poisonous/venomous. If you spread your findings, we can hopefully alleviate the negative attitudes towards saving this animal by domesticating it.

      To all of you who are against domesticating the slow loris, tell me: has putting it on the endangered species list and protecting it by legal recourse actually stopped the illegal trade of the slow loris? The answer is NO. Keep up your “save the animals” and “we speak for those who can’t speak for themselves” mindsets and watch as it does nothing to prevent the extinction of this animal.

      1. Ignorant commentry Jeff! Even the best zoos in the world with the best vets have NOT breed this species in captivity with any success as yet and loris have been in captivity for over a hundred years now you would think if its that easy they would have figure it out. Instead they have to keep replacing the ones that die in captivity with more illegally caught or confiscated imported animals. So good luck to any amateur!

        There is a difference between captive breeding and ‘domesticating’. If you can’t do the first one yet how the hell are we supposed to do the other? It is the illegal pet trade killing them off as it is. Domestication isn’t even a feasible option for the well meaning or ignorant people who want to justify having one as a pet.

  6. I would like to point out that zookeepers working with these animals speak of even simple bites as “events that take 6 months or longer to recover from”, and always wear industrial strength welders gloves whenever they have to get close to the animals.

  7. Hi all, I was bitten by a Nycticebus pygmaeus 3 days ago, while I was getting a blood sample in the zoo where I work as a vet. The bite was quite painful but nothing serious. I desinfected thorougly the bite flushing the very small holes with clorhexidine and an antibiotic ointment. The bite get a moderate inflamation during the next few hours and it did not coagullate easily and some blood was still flowing 3 hours latter.
    Next day all inflamation was gone but I noticed a marked hematuria (blood in the urine) for the next two days. Today just traces of blood could be detected by urine straps. Otherwise I have felt completely normal. I have find your article and I was quite surprise about the hematuria reported in the first bite case in 1972.

    Jesus Recuero, DVM
    Bioparc Fuengirola

  8. Thanks Jesus.

    That is interesting and I’m glad that you are feeling better with no complications. Too bad I’m not a medical student, or I would have compiled data from people being bitten by slow loris and publish a paper on it! Published data for loris bites are scarce.

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