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Episode 307: Surprisingly venomous Slow Loris

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Teddy bear or primate? The super cute slow loris (image from www.japantimes.co.jp)

There is no better name than slow loris for this small, shy nocturnal primate. They move at a very unhurried pace, foraging in the night for fruit, nectar, insects, and even small mammals. Their uncanny ability to hold almost completely still helps them vanish into the trees they call home, avoiding predators and competition from other lorises.

Slow lorises are a group of primates belonging to the suborder Strepsirrhini, made up of lemurs, galagos, pottos and lorises. The range throughout Southeast Asia and currently they are at least nine subspecies of slow loris recognised today:

  • Nycticebus coucang, the Greater Slow Loris
  • Nycticebus javanicus, the Javan Slow Loris
  • Nycticebus bengalensis, the Bengal Slow Loris
  • Nycticebus menagensis, the Philippine Slow Loris
  • Nycticebus bancanus, the Bangka Slow Loris
  • Nycticebus kayan, the Kayan Slow Loris
  • Nycticebus borneanu, the Bornean Slow Loris
  • Nycticebus hilleri, the Sumatran Slow Loris

The pygmy slow loris, once a part of the Nycticebus genus was moved in 2022 to its own new genus, Xanthonycticebus, because genetic analyses revealed it had diverged away from the other lorises much earlier than thought.

Lorises first appear in the fossil record in the Miocene period in Thailand, with just a single tooth similar to the dentition of modern day lorises found. Their ancestors evolved in Africa, and it is hypothesised that lorises reached Sundaland, the ancient land mass that today corresponds to Southeast Asia, when the Sunda Shelf was exposed by decreased sea levels, creating a land bridge that allowed animals to reach the islands off the mainland.

Tiny but toxic: the venom of the Slow Loris

It is a very unusual thing for a mammal to be venomous, and even more unlikely for primates. There are only 7 mammals known to be venomous, and out of those the slow loris is the only venomous primate. Interest in slow lorises began when researchers heard folkloric tales of the potent bite of the slow loris, with local traders in slow lorises for the captive trade frequently and tragically removing their teeth to prevent bites. A scientist name Alterman was the first to prove that slow lorises were venomous by extracting the venom of captive slow lorises and injecting it into mice. He also determined that their venom was only deadly to the mice when combined with secretions from the slow lorises branchial gland, a small swelling near the elbow. These secretions activate the toxins of the venom, allowing it to become potent. Scientists are still trying to detangle the compounds in venom, although they have identified a molecule that closely resembles the allergy causing component of cat dander.

When threatened, slow lorises lift their arms quickly and lick the oily secretions from the brachial gland on their upper arm. This mixes the oily secretions with their saliva and this pools in their specially adapted comb like teeth, which are sharp enough to slice through bone. The toxins are then deposited onto their fur, wrapping them in their own venomous cloud. They can also bite, injecting their venom right into their aggressor for a nasty shock. Since one of the predominant compounds in slow loris venom is like cat dander, they can often cause allergy like symptoms in the unfortunate creature that gets bitten, such as swelling and in extreme cases anaphylactic shock.

The venom system of the slow loris. Figure A shows the warning colouration on the fur on the slow loris. Figure B shows the defence position of the slow loris, lifting its arms above its head so it can reach the brachial gland, the location of which is shown in Figure C. Figure D shows the specialised dentition of the slow loris, with the tooth combs designed to trickle the venom out onto the fur. Image from Rode-Margono and Nekaris, 2015)

But why do these cute, cuddly little primates need such a toxic feature? In so many venomous animals, venom is used to kill prey, but slow lorises are predominantly frugivores, and any animals they do eat they can overpower pretty easily. Although admittedly they are very hard to study, there is no evidence from the field that Lorises use venom on prey. Venom tinkering scientist Alterman was convinced that they used the venom to deter predators, but again, there is little evidence of this in the wild. In zoo studies, loris venom was coated on foliage and presented to sun bears, tigers and civet cats, all of which were repelled by the venom. However, in other studies, scientists presented orangutans, known predators of lorises, with venom coated foliage, and they didn’t hesitate to eat the foliage without pause and without any health issues. There is also good evidence that coating themselves in venom can reduce the incidence of parasites. When scientists exposed arthropods like spiders and ticks to slow loris venom, most of the trail animals died, and all of them showed reduced activity. Studies of wild lorises have revealed that the levels of ectoparasite infestation in their fur is significantly less than most other primates.

Although there is some evidence that slow loris venom can repel predators, anecdotes from keepers of captive slow lorises revealed that the cute critters were often using their venom against their own. Researchers in Indonesia radio collared 82 Javan Slow lorises to track their movements and would recapture the animals every few months to check their health. 20 percent of the Slow Lorises they encountered were suffering from nasty wounds, and the researchers deduced that this was down to scraps with other Slow Lorises, using their venom to settle scores and keep their territory defended. Some of the Slow Lorises were so aggressive when handled that they were only measured a handful of times by researchers brave enough to put their hands in the danger zone. Slow Loris bites can be nasty for humans and there has even been one death from anaphylactic shock, but they pack a nasty punch for other Slow Lorises. The venom causes necrosis, with some slow lorises losing an eye, part of their scalp or even their face.

An unfortunate slow loris with a bite from a competitor, causing necrosis to the head (www.nytimes.com)

Cute but should never be caged; the threats facing Slow Lorises

All of the Slow Loris subspecies are endangered. Like so many species in Southeast Asia, catastrophic forest loss is a big concern, but it is the illegal pet trade that is really devastating the species. For a long time, this shy species was virtually unknown to the public, but in recent years viral social media posts displaying slow lorises, mostly illegally caught from the wild, as ‘cute’ pets. Sadly, but not surprisingly, the slow loris trade is incredibly cruel. Once poached from the wild, they will have their teeth extracted with pliers to prevent them biting poachers and the eventual owners, and this process can often cause death through infection and blood loss. They are then transported to markets in terribly overcrowded, dark containers, with mortality rates from these trips anywhere between 30 and 90%. If they survive this ordeal, they are sold either into traditional medicine markets, where they are killed for their body parts that some cultures believe cure disease, or they become pets and kept in unnatural conditions. A common trend was to ‘tickle’ the slow loris, which would result in them lifting their arms above their head. As we know from studies into their venom, this is actually a stress response, allowing them to reach their brachial gland to spread the venom around. Instagram has been a massive driver of demand for pet slow lorises, and if you see one during your scrolling, please report, as it is almost guaranteed that this is an illegally caught wild specimen, removed from its rightful home in the wild. Its hard to track slow loris populations in the wild, and even harder to track the illegal trade routes and the locations poachers are taking them from. You can be a conservation hero with just a few clicks!

The viral social media post depicting a slow loris being ‘tickled’; in fact this is a stress response. (image from theconversation.com)

It should go without saying, but lorises do not make good pets. They are nocturnal animals, but are often kept in bright artificially lit conditions, causing pain and suffering for such sensitive animals. They also cannot express natural behaviours such as foraging in the tiny cages of their captivity, and their complex natural diet of fruits and insects is rarely provided, causing malnutrition, infection, diabetes and bone diseases. They are without doubt very cute and cuddly, but please, stick to a cat or a hamster to meet your cuddling needs.

The dreadful trafficking conditions slow lorises experience in cramped trucks (image from us.blastingnews.com)

Conservation Optimism

Although the illegal pet trade is decimating slow loris populations, it was also the factor that brought the conservation needs of the shy little primate into prominence. Over the last 10 years, there have been a lot of policy changes, including a 2007 change of the Nycticebus genus to Appendix 1 of CITES (Convention on International Trade in Endangered Species of Wild Fauna and Flora), making it illegal to conduct any trade in slow lorises or their body parts. Prior to 2008, the slow loris species recognised were listed as Near Threatened by the IUCN red list, but were upgraded to either Vulnerable or Endangered, hiking up their conservation priority and research money. Although these were positive moves, there is still a lack of enforcement across the range, and charities and governmental organisations are looking to improve this by providing funds and training for wildlife officials working in the slow loris ranges.

Tackling the illegal poaching and trade of slow lorises is essential but proving incredibly difficult and so a lot of conservation efforts focus on the rescue and rehabilitation of slow lorises cruelly trapped by such an insidious market. Organisations like the International Animal Rescue (IAR) run a sanctuary and rehab in Java, with a vet clinic, spacious enclosures for socialisation and a public education centre where they can teach locals about the plight of this little teddy bear primate, amongst other species. Check out their slow loris work at https://www.internationalanimalrescue.org/projects/slow-loris.

A slow loris being carefully rehabilitated and fed the correct diet with the right nutrients (image from The Dodo)

Generally, slow lorises don’t thrive in captivity, and so the aim is to release as many of them into the wild as possible. Sadly though, the success of this can largely depend on whether the individual kept their teeth, as their well-adapted tooth combs are so essential to their natural behaviour and territory defence in the wild. In this case, lorises are cared for as best as they can be by dedicated primate keepers in zoos and sanctuaries and used to educate people about the tragic tale of the pet trade. Research is being conducted into slow loris behaviour, and the San Diego Zoo has written a husbandry guide and supported rescue facilities to provide the best care.

A rehabilitated slow loris taking the first tentative steps towards a new life in the wild (www.irishnews.com)

Awesome videos!


Grow, N.B. Wirdateti. and Nekaris, K.A.I. (2015) ‘Does toxic defence in Nycticebus spp. relate to ectoparasites? The lethal effects of slow loris venom.’ Toxicon



Nekaris, K.A.I. Campera, M. Nijman, V. Birot, H. Rode-Morgono, E.J. Fry, B.G. Weldon, A. Wirdatedi, W. and Imron, M.A. (2020) ‘Slow lorises use venom as a weapon in intraspecific competition.’ Current Biology

Nekaris, K.A.I. Moore, R.S. Rode. J.E. and Fry, B.G. ‘Mad, bad and dangerous to know: the biochemistry, ecology and evolution of the slow loris.’ Journal of Venomous Animals and Toxins Including Tropical Diseases.

Nekaris, K.A.I. and Nijman, V. (2022) ‘A new genus name for pygmy lorises, Xanthonycticebus gen.nov. (Mammalia, primates).’ Zoosystematics and Evolution.

Nekaris, K.A.I. and Starr, C.R. (2015) ‘Conservation and ecology of the neglected slow loris: priorities and prospects.’ Endangered Species Research

Rode-Margono, J. and Nekaris, K.A.I. (2015) ‘Cabinet of curiosities: venom systems and their ecological function in mammals, with a function on primates.’ Toxins


November 23, 2022
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